Idle problems
 

I've got a 1985 that varies its idle RPM from 550 to 750, in park and in drive. Car runs great above 750 rpm. New plugs, cap, rotor, and MAF sensor. Can't detect any vacuum leaks. I was told that the 1985 did not have a power or burn-off relay for the MAF sensor. Any ideas. Thanks.

RE: Idle problems
 

Vacuum leak. 100% probability.

https://www.corvetteforums.com/m_37283/tm.htm

print it out, put it in the bathroom.

RE: Idle problems
 

[sm=welcomesign.gif]

My C4 '87 runs at 500 in park or drive(foot on the brake). Not sure why your's varies...

Ask Mech259 [8D]he might know...

RE: Idle problems
 

The answer to your burn-off relay question is also in the article. Fifth post (p. 23). It won't matter for yours however; we already know whatcha' got there...

RE: Idle problems
 

Throttle plates probably need cleaning. When they get carboned up, it is difficult for the plates to seal in throttle bore and the ECM has trouble controlling idle.

RE: Idle problems
 

Thanks for all of the input. I guess I'll try cleaning the throttle plates next. I read the article and tried the propane with no luck of locating a vacuum leak. The car has 30300 miles on it and is like new except for my idle problem. I've set my idle at 700 rpm in park and the car purrs, but at 500 it surges to 700. What do you guys think of an EGRissue. I currently do not have any codes stored or a service light. By the way I also have a 2000 and a 1979 vette. Thanks.

RE: Idle problems
 

One more thing to note, this is a 1985 car that has had about 2000 miles put on it in the last ten years. Thanks.

RE: Idle problems
 

30K doesn't seem like enough distancefor avacuum leak to develop. I can't imagine carbon build-up either.

...or anything else failing, mechanical-wise. Rubber and other organic fiber compounds - vacuum hoses and gaskets,COULD fail, given the time period.

So I gotta' stick with an intake leak somewhere. Get back on this one tho'... I'd really like to know on this one.

RE: Idle problems
 

I agree with cleaning the throttle body and the IAC also. You can usually hear vac leaks....like a hissing sound.

Does it make a difference if the engine is cold or hot? Usually a vac leak will disappear once the ECM goes closed loop.A easy test to do if you have an ohm meter is to check the resistance of the injectors hot and cold.

RE: Idle problems
 

the burn off relay is behind the breadbox check the fuel filter and like said above clean the plates

RE: Idle problems
 

That's a negatory there, rrt.

My '87 had a ton of leaks, and the only one I ever heard was the one from the incorrectly seated cold start injector, AFTER top end re-assembly.

RE: Idle problems
 

Thanks for all of the good info. Cleaned the throttle body and still have the idle problem. No indication of vacuum leaks using the propane method. The erratic idle only occurs after initial warmup and once again if I set my idle at 700rpm the car runs great. I think I'll check the power and burnoff relays next.

RE: Idle problems
 

I missed that you got no codes. Confirms vacuum leaks. Nothing else will cause your symptom. Nothing.

Any motor gettin' air that's not mixing with the gas (or not getting 'registered' to mix with the gas), will rev when the air mix leans out.

THEN...

The carb'ed motor pulls more gas (no throttle change), and it revs down.

The TPI revs as the leaner mix passes (no throttle change), the computer gives gas for the revs, and it slows back down - cause no acceleration.

Tunin your carb, you increase the fuel from the jets, the revs go down.

My neighbor's lawn mower did it.

Ya gotta' get a torque-on. The bolts, that is... Either that, or pull the plenum TB, runners, and intake. If you don't, you will get carbon fouling.

Gas is not what burns. It's the oxygen. Rocket fuel is liquid oxygen.

RE: Idle problems
 

Once again thanks for the info. Thought I had it fixed when I pulled and cleaned the Idle air control, but it started acting up again at idle. One thing to note is that my air plenum was pretty sooted up when I pulled it to clean the throttle body. I am picking up a lower and upper intake gasket set today. Any suggestions of what else to check while I have it apart. Thanks.

RE: Idle problems
 

Get some parts cleaner. The gallon size, with the basket in it. Get a couple of paint brushes, for paintin' on the parts cleaner. Get a low-rise plastic tub that the intake will fit in. That catches the cleaner fluid as you brush it on. Get a bottle brush for the plenum and the runners - they got a ton of carbon.

Get some Trans-X for the injectorO-rings. If they're not visibly cracked, they'll re-seat just fine if they've been allowed to sit in the Trans-X for 6 hours. AND KEEP A FINGER ON THE INJECTOR CONNECTOR CLIPS WHEN REMOVING, TO PREVENT BALLISTIC DISAPPEARANCE. Someone else called 'em Jesus clips, but don't use his name unless it's from the heart;).

You might need an 8" long x 1/4" drive ratchet extension, with a 1/4" x 3/8" adapter on the end, to get the passenger side, rearmost intake runner-to-intake manifoldbolt. And possibly the forward-most passenger side bolt also. THEY ARE TOUGH!

Put all bolts back in the original holes as soon as possible, until ready to clean the bolt and hole itself. Penetrating lube with the spray tube works pretty well for the hole. You do NOT want to mix up bolts. I don't think there are two alike, except the distributor cover (maybe...).

Do a total dry (trial)fit at re-assembly, without gaskets. Trust me.

Put a grease film on all gaskets when you do final re-assembly. And they gotta' be SURGICAL clean.You don't want ANY air leaks. Use metallic thread lube - can't remember the metal. Anybody?

When removing parts, make sure there's NO 'jam' in the bolt heads. YOU HAFTA make sure the socket is well seated in the bolt. Especially in the hard-to reach spots. One 'round-out' in the wrong place is gonna' triple your work time and cost.

Don't drop any bolts in the distributor hole;). Make sure the cold start injector is properly seated;). If you miss, it won't take long to find out what's up with that.:DAfter you get that one right too, you won't believe the difference.[sm=gears.gif]

[IMG]local://upfiles/5243/2F6BB4F995B64BF9ABD34BA463A5BE0C.jpg[/IMG]

RE: Idle problems
 

Thanks, Ive got a busy night ahead of me.

RE: Idle problems
 

Night, huh? You probably could if ya' really wanted. But don't.

It took me 3 weekends+ ~ 55-60 hours. The dry fit, putting each bolt back in the hole as you go, cleaning out bolt holes with lube, AND A SHOP-VAC (call it over-kill if ya' want), cleaning bolt threadswith a toothbrush, and stopping to take pics and write stuff down, really adds alot of time.

But afterwards, youKNOW when you pull the trigger, it's gettin' ready to play SWEET music.

Unless you didn't properly seat the cold start injector.[:@]Only took a minute to figure that out tho'...:).

EDIT:
Put a piece of tape extending from the distributor rotor to the underneath outside of the rotor housing. THEN, before pulling the distributor out, cut the tape between the two. The rotor will turn as you pull it out, independantly of the shaft, and the tape will 'UN-align. It will 'RE-align', as you re-insert.

Also, mark the shaft in relation to the manifold mount hole, and score it with a screwdriver, along with the shaft. You can also put a piece of tape from the base of the rotor housing, to the firewall top. You want to have as many reference marks as possible. And remember how it turns as you pull it out, because you have to turn it back before going back in. the cam drive gears are helical.

RE: Idle problems
 

Spent a good twenty hours pulling and cleaning the intake system. Still have the same idle problems and now Ive got a little hesitation when putting the pedal down. Still no codes present. One thing to note, when the car is idling erratic and I remove a vauum hose, any vacuum hose, it smooths right out for a couple of minutes before going back to its erratic idle. Any thoughts. Thanks.

RE: Idle problems
 

If it smooths out for a moment, that seems to mean the computer is readin' the air well (and unfortunately, the leak too).

Did you see any places during disassembly where the gaskets were compromised? Worn through? I guessin' you got a different leak now, from somethin' not seated right. ESPECIALLY if no diagnostics codes are tripped.

If you can't find it, you're gonna' have to crank the idle speed to get a steady idle speed, and hit it again with a propane torch.

RE: Idle problems
 

Old gaskets looked to be in good shape with no areas compromised. I'll hit it with the propane again. How do I troubleshoot the computer if the whole thing has been the computer from the start. thanks.

RE: Idle problems
 

The parts retailer will usually plug in their scanner for free. If you do that, ask them if anything in the computer, and only in the computer,can get by their scanner.

Do not ask themabout a vacuum leak; they'll say if you can't hear it, there ain't one. And that ain't the case with a TPI. I know ya' don't wanna' hear it after all the intake re-workin', but I think you didn't get two parts seated properly.

Was there any part you weren't sure of when re-installin'? At all?

Thegasoline delivery process, and the ignition (spark) process, by themselves, will not cause the lopin' idle - only airflow process can do this.

RE: Idle problems
 

I have a code 43 and a code 44. The 44 more than likely is due to the 43. I can read these myself by jumping the appropriate ports in the diagnostics port. First I'll try the propane and if no joy I'll have to replace the ECM BASED ON THE CODE 43. THANKS.

RE: Idle problems
 

I do NOT think they are related.

As far as the 43 code, I would NOT spring for a new ECM, until testing for a signal for timing retard. The 43 code says retard has been on too long (which would mean there IS a signal)OR ignition retard system failure (no signal). TEST FOR SIGNAL FIRST!!!

If 44 can mean vacuum leak, I'd go that way first. Since both codes COULD be because of ECM connections, and not necessarily a bad ECM, check all the leads with a probe.

Even if there's some short circuits to the ECM, you still got the loping idle.

Check the service manual for both codes, to see if it says go after one of the two codes first. Or did you already do that?

RE: Idle problems
 

Just checked it with the propane with no evidence of a vacuum leak. I think I'll pull the ecm and reboot it. Thanks.

RE: Idle problems
 

Code 43 can be caused by bad knock sensor or broken wire to the knock sensor which is just in front of your starter.

RE: Idle problems
 

The knock sensor wouldn't affect my idle, would it. I rebooted the ecm last night and that didn't do anything for me. I think I'll pick up an ECMtoday to at least use as a trouble shooting tool. Thanks for the help.

RE: Idle problems
 

Knock sensor won't affect idle. It is used by spark timing control to retard timing when detonation is picked up by sensor. Code 44 is a lean code and maybe the result, not the cause of poor idle problems. What kind of O2 readings do you have at idle and cruising speed?

RE: Idle problems
 

Here's your ESC signal test:

Take the idle speed up a couple of hundred rev's over idle - 900 - 1000. Hit the block quickly on the passenger side a couple of times with a screwdriver. If the idle drops, yourESC system works (or at least has a signal complete circuit.

If there's no drop, there's no signal gettin' to the computer to retard the timimg.

RE: Idle problems
 

sounds to me like your running lean, I also wouldnt give up on the vacuum leak possibilty until I was 100% sure it was not the problem[X(]

RE: Idle problems
 

Tearing the intake apart again insearch of a possible leak. Thanks.

RE: Idle problems
 

Imissed the second page:)....... change your burnoff relays right behind the battery on the fire wall 15mins-$15 easy cheap o2 sensor if not new replace it cheap easy, the maf should be pulling 4-8 grams per second past it if too high the ecm will try to compenstate by starving the car and lowering the RPM's if its at 9grams or higher change it, also if you know somone who has and extra one you can swap it and see if that changes it. keep in mind mid america has a the ecm for $329.00 but super expensive.
also check the connections to the relays and the connection to the MAF , also with the engine idling, try tapping the MAF sensor with the handle of a 6" screwdriver. I don't mean belt it with a 3 pound hammer, just tap it lightly, if the engine stumbles with ever tap=bad
ECM is the last resort it may be bad and hunting for the idle all on its own but UNLIKELY:D:D:D
:Dhope this helps you bro!!!:D

RE: Idle problems
 

ment MAF for $329.00 sorry;)

RE: Idle problems
 

That's what I was thinkin' too there, '84. Ya' don't wanna' hear it after you re-do the entire intake, but I got no clues what else could cause lopin' idle with no codes...

ibelew, did you get a good grease film on the gaskets at re-assembly? Grease film helps seal, AND helps hold the gaskets to the intake runners, when you're puttin' the plenum back in between the [still-loose] left and right intake runners... And the TB passages gotta' match up with the right gasket openings. What a pain that was[:@][:@][:@].

At the same time, you don't wanna' over-torque any bolts in the aluminum either.

RE: Idle problems
 

OK, just finished putting my second set of gaskets in. Still have the erratic idle. If I disconnect the ESCthe idle smooths out. I've got a new MAF sensor, new IACplugs, wires, cap and rotor and two sets of intake gaskets. I'll check out a burn-off relay tomorrow. Where is the MAF power relay located. By the way I plugged a new ECM in with no luck so I returned it. I think I'll go tune my 79 up since it's alot easier to work on. Give me some good advice guys. Thanks.

RE: Idle problems
 

Chevrolet Corvette Check Engine Light
Q. I sure hope you can help me. I have an 1988 Chevrolet Corvette with an L98 engine with 113,000 miles and automatic transmission with little, if any problems mechanically. The check engine light is intermittent. Some days its on and others its off. I have taken it a few mechanics and all say its a wiring problem, probably a short somewhere.
http://z.about.com/d/autorepair/1/0/Z/L/mechanic.jpg
But they are unable to locate. I have noticed when the check engine light is on it is giving me a code with some thing to do with the MAF sensor or the burnout circuit relay. All of that has been changed so its got to be a wire problem.
I noticed a green wire on the drivers side near the engine block and transmission. I have attempted to ground it but is a hot wire. I know a green wire comes from the MAF sensor but unsure where this green wire goes.
I don't know if this is the problem or this needs to be connected somewhere. Do you have any reference material showing wiring locations and if there is any remedies for this? Any help?
Thanks,
Michael
A. Have you tried a dealer? There are a few service bulletins out pertaining to this code and replacement of power and burn off relays with a new design relay.Number: 88-251-8a
Section: 8a
Date: June, 1988
Subject: Intermittent Connection To The ECM
Model And Year: 1988 Chevrolet Passenger Cars And Light Duty Trucks T: All Chevrolet Dealers
A condition may exist in which the female terminals in the connector to the ECM do not make a solid connection to the male pins in the ECM (see illustration). This can result in an intermittent condition, in any circuit operated by the ECM. The Service Manuals direct a check of connections any time an intermittent condition is found, and this may be the cause of some of these conditions.
Visually inspect the terminal using a flashlight, or use a .95 mm pin gauge. The gauge should not pass freely through the female terminal. Do not probe the terminal with anything other than the pin gauge, as probing could damage the terminal. If the female terminal does not grip properly, replace the terminal with P/N 12020757. General directions on wiring repair are shown in Section 8A of the service Manual.
Number: 89-327-6D
Section: 6D
Date: May 1991
Corporate Bulletin No.: 138111
Subject: Intermittent No Start, Long Crank, Stall, Or Engine Surge
Model and Year: 1988-1989 Corvette
Condition:
On the 1988-89 Y Car, the engine may have intermittent no start, long crank times, may start and stall after start, or may have engine surge or rough running. No codes will be set, and no trouble can be found using normal diagnostic procedures.
Cause:
The relay used for production, P/N 14103304, may not conduct enough current to allow the Mass Air Flow (MAF) circuits to operate properly. The relays will test OK.
Correction:
Both the MAF relays (Burn-off and Burn-off control) should be replaced with relay P/N 14089936. This relay is serviced with a bracket, which is used only for 1988, and can be discarded for the 1989 model year. The location of the relays is shown on page 8A-20-9 of the 1988 and 1989 Y Car Service Manual.
Pad is currently available from GMSPO.
The O2 sensor may also be carbon-coated because of this condition. To clear the carbon, apply the parking brake, and allow the engine to warm up to normal operating temperature. Then hold the RPM at 1,800 RPM for three minutes.
I KNOW ITS A LOT TO READ BUT IT WILL HELP YOU UNDER STAND THE PROBLEM A LITTLE BIT BETTER TO COME TO THE SOULUTION
COURTESY OF ALLDATA:D:D

RE: Idle problems
 

Hello, wires are good. Installed new burnoff relay with no luck. No vacuum leaks. Idle is still erratic until I pull off the connector to the ESC. Plan on installing a newa new knock sensor tomorrow since it failed the ping test, I think I'll have a spare ESC standing by as a trouble shooting aid. What else do you guys thinkI should check.Thanks.

RE: Idle problems
 

This knock-sensor test failure will have an effect on your timing.

Normally it would retard the timing when a vibration (knock) is detected. You'd have less power. But didn't you before have a code for 'too long retarded timing', or something like that [no signal]???

RE: Idle problems
 

Hello. I had a code 43 that led me to check the knock sensor and it failed the test you recommended. I need to start back probing some pins on the computer. I can't afford to keep throwing parts at it. I still have the erratic idle but not as bad. The car runs great when accelerating but crappy at cruise and idle. Thanks.

RE: Idle problems
 

Does it feel like it's surging at cruising speed? If so, heres something to try...temporarily disconnect the vacuum line going to the EGR valve and plug it with something. You'll need to disconnect it at the EGR solenoid because you won't be able to get your hand under the plenum to reach the egr valve.Take it for a drive and see if it runs any better at cruising speed.

RE: Idle problems
 

Do you have a K&N filter?