Hey all! Newbie here with a 88 C4, 51K miles and issues.
I got it Monday, delivered from Massachusetts. It runs SUPER rich & rough. It runs fine off idle & while driving, but on idle/stopped it runs very fat.

Car has been sitting for about 7-8 years, clear history & proof its been sitting for years, so I assumed its a bad fuel problem & all the issues with that. Arrived with less than 1/8 tank of gas that smelled semi-recent. Fuel pressure reads correctly with the key on, idling and with the vac connection unhooked. Plugs & oxy sensor were flat out black with fuel, swapped them out. Put in new plug wires, replaced the "new" cap/rotor, coil, ignition module & wires with better brass parts. TPS reads correctly. Still the same, maybe slightly worse. The MAF was replaced before me with a Bosch unit, installed upside down (??) so I put in a new GM unit. Checked for vac leaks along the intake & plenum, none. Assumed the fuel pressure regulator went bad, but it shows 42lbs with key on, 38lbs running & goes up with vac disconnected.
I am at a loss. Car flat out smells of fuel, its clear. I'm unloading the shotgun of parts at it this weekend:
Upper intake/plenum gaskets
New fuel pressure regulator
New flow tested injectors
New MAF relay, air intake temp sensor, coolant temp sensor, 180* thermostat
I even have a new prom from PCM of NC with the cold start injector shut off.

Everywhere I look, someone has been there so this is not a new problem to the car. Oddly, when I dropped the PCM to order the new chip, I found it has been out before (the prom cover was taped back on, screw threads were stripped out). The MAF relay had been replaced, the cap was replaced also with a cheap unit.
What are the chances the computer itself is bad?? I dont want to think that, but it should be showing a check engine light for something by now. I can check that easily I guess, but dont like running it in the current condition. Once I "unload" the shotgun of parts I'll trip it on purpose, but I have a feeling (?). I have ordered the Moates pcm cable & plan on trying out the TunerPro software for after the new parts, but not sure. While its apart I can verify all work done, but at 51K miles I find it hard to be something major??

Lots of info, lots I left out, but any ideas? The main thing that gets me is no check engine light..hmmm...

 

This might help. Check the idle air control {VAC} valve, sounds like its gummed up or stuck. they can be cleaned or just replace it. $30 - $50

 

Thank you! That makes complete sense also. I did look at it & there is a replacement in there, but I did not even think to actually pull it out & look.
I did find a AC Delco on Amazon for $45, score

 

You could check the O2 sensors for proper output. I don't know how to check this but it sounds like it might not be coming out of open loop control during the initial startup and just staying in that all the time.

 

Hope your making progress on your baby, you did not mention if you got any error codes stored in the ECM thats the first step.There is a website at wwwcorvettebuyers.com that shows how to read codes and what the codes mean, Your ECM could be bad, there is a code for that, but i have gotten this code off an ECM before an it checked out fine, be sure ECM connectors are clean and tight, not sure if you have the right ecm you might want to track down the numbers on it. You can have errors that wont trigger the check engine, its rare. I have used after market proms in ecms and allways had good luck 180 degree thermostat, bump up the dist. timming 2 or 3 degrees up grade of gas and got 2 more miles per gallon. Hope you dont have leaky fuel lines on top of the fuel tank worth a look and smell. this condition might be the reason it was parked or not. Dont get to discouraged, think of this as a learning experance. I had GM schooling in early 80s on ecms with carburetors but not injection systems, still learning. Hoped some of this helps, keep posting on how its going.

 

Thanks for all the support!
I unloaded that parts cannon at it, lol. Also noticed the intake had a good sized oil leak at the rear, so I did that while I was in there...I added a lot of non-related parts while I was in here!
Its all back together today & I fired it up. I am waiting on the valve cover grommets to arrive for the new valve covers, but went for it. It ran rough at first, but I am trying out the moats OBD1 program & Tuner Pro and was able to see the TPS was reading low (.38). That program was worth its weight in gold just for speeding that process up!
Lots of new parts, but I adjusted the TPS to .67 and set base timing at 9* and things cleared up nicely. Its not dumping fuel non-stop anymore, score! Having some issues on start up and a high idle. It also wanders a little, but there is a massive vacuum leak with the PCV system just hanging in the wind till I get the grommets. I did kind of do a stupid thing & lowered the idle speed screw after it was warm, causing me to re-adjust the TPS & go on a endless circle between the two. Ooops! For now I put the idle speed screw back to where i guesstimate it was & set the TPS back at .67.Kind of unsure on what I need to set first but I'll figure that out.
Success I'd say! Its not running as smooth as it should, but between the PCV leak & me messing with the idle speed I think I'll get there. Found a couple small issues while tearing it down (thermostat stuck open, valve cover & intake oil leaks, RTV on the TB gasket, ect) so the parts cannon was worth it. The old injectors were in bad shape too. I pulled the filters off 3 of them & 2 were full of junk, one was clean.

Getting there! Road trip to Bowling Green is the main goal, once I get her all set up!

 

I used to be all Chevy then I fell into the Mustang trap, haha. Been so long since I got to play with a SBC that I forgot more than I ever knew, so this was fun so far. Amazed at how hard it is to get parts that used to be on shelves, but fun. This went quick too. Got it all torn down & cleaned Monday. Intake gaskets didn't arrive till Tuesday at noon & I fired it Wednesday morning.

Dont look too close at how dirty EVERYTHING is, but it is spotless inside. It has 51K on it & I was really doubting it, until I got it open. Just needs aome elbow grease & time & hopefully look as it should.


Monday

Tuesday night

 

Looking good and it sounds like you're making quite a bit of progress. Thanks for the feedback.

 

Good job, hit the nail n the head. Hope you like driving it more than working on it, nice straight looking car.

 

Thanks! Lots of tinkering, but its almost there. The rough/high/low idle is clearing up after a new TPS & many tiny throttle plate adjustments trying to get the IAC counts down. Still a tick high but better. Took it on a 20 minute "danger drive" & all went well. It did stall when I got back home & put it in park, but I think the new fresh gas is still working its way through. Still seems to have a slight miss on idle but I'm kind of suspecting the plug wires, but that may be the old gas too. I put the cheapest Moroso wires in there & wasn't impressed with them, wouldn't doubt a loose connection. Easy fix there anyways!
Getting there!