I would run a bottle of Techron through it since it's probably having some bad gas issues.

 

Darn car is driving me nuts! After much tinkering, it is running great but wandering idle is still a problem. I just finished putting on a new BBK 52mm throttle body (not by choice, the old one had some issues with the coolant crossover bolts snapping off). I got a little upset & didnt set minimum idle/air rate after putting on the new TB so it was idling high in open loop, roughly 950 or more. It just wanders around, up to 1400rpm sometimes then back to 950ish and it just isnt running smooth.

Parts wise, whatever it is, it is new, ugg! TPS is set at .55, IAC counts are now 30-50 so thats close I think. Airflow rates at idle are 3600ish. Timing is set at 6 or 8, whatever factory is. I've been all over the vacuum hoses so I doubt that (?). Driving, the car is 100% fine, but the nervous idle makes me nervous! It should run smooth as glass for the low miles on it.
Getting frustrated & feel I'm overlooking something very simple, any ideas? I did a data log with the Moats software but not sure how to post it here or if anyone uses that, but I've gone pretty far into that & doubting everything I do now.

Theres nothing mechanical that can cause rough idle correct? While the top end was apart I did just verify no rockers were loose but that was about it. I suppose I could get the timing light back on it & watch it as it idles, maybe a distributor issue? I dont know the maintenance history of the car, but this doesnt look to be a new problem since everywhere I look, someone has been there before. Hmm, explains the low mileage, lol!

Any ideas? I'm open to anything at this point! I actually have a cart full of parts at Summit ready to carb swap this thing for when I totally lose my mind, haha! Really really dont want to do that, but I'm close.

Thanks!

 

I did find a deal on some new wheels/tires for the Vette, so I'm not that mad at it! They look a little odd in the pic, but much better on the car. Once its going I'll get her all cleaned up & show off some pics

 

Dear QuickNick. Sorry all your work hasen`t ended in perfection, I haven`t played with this setup before but they are all about the same idea, I can only give a few suggestions, not sure of everything you have done or checked. I would start with pulling all vacuum lines from manifold and plug, pvc brake booster egr, check egr to make sure its working correctly (not Leaking ) that can give a Vacuum leak. It sounds like its warming up and in closed loop, I wonder if your new fuel injectors are not plugging from the left over bad fuel causing rough idle condition, maybe pull clean and reinstall. There`s not much you haven`t replaced, It would help if you had a check engine light but that only happens with a falt or inop sensor not poor reading. I have replaced ecm`s before when they said they were bad, new one worked fine. then the one I replaced checked out fine. So i`m thinking there was a problem with maybe the wiring harness, so that`s why I think sometime`s where there are problems in the pcm system it could be a good idea to pull the harness and clean the connections to the pcm unit. Can`t think of anything else right now. Helpful maybe? Good luck..

 

Thank you!
I spent a solid 10hrs picking over stuff today & have a slight improvement. I verified timing at 8* & made sure it was advancing correctly, then went looking for grounds to clean up. I even added a ground strap from the crossmember to the cylinder head. Pulled every relay under the hood & swapped them around (worth a shot) and cleaned contacts for hours! I attacked vac lines with a Mighty vac & replaced anything questionable.

I think your on the right track about a bad/loose wire somewhere. As I was timing it, it was running fine then started the random miss. I tried shaking wires around near the distributor thinking I was on to something but couldnt make it go from good to bad on command. Think I need to spend more time shaking wires around with it running.

I was doubting the PCM, but after running the Moats/Tuner Pro software on it I can see things working. It still hasn't triggered a check engine light though all of this, but I can cause one if I want, so it must take a lot to get it to go on! Thinking I'm just going to start driving the thing & see where it goes. I dont know, maybe its just not seeing enough run time, I usually try a few things then take a trip around the neighborhood, no real world driving. Just a thought.

 

Ya drive it, it does wonders sometimes,it can only get better or worse. the random miss might go away. Good luck, nice wheels.

 

It wouldn't hurt to run a couple of bottles of Techron through it just to clean everything up in the fuel system.

 

I've followed this thread all the way, very interested, I have fought some of the same battles with my 87. You mention the car sat for 7 years. So it was parked in 2014 or 15, or at 27 years old. 51,000 miles in 27 years is slightly less than 2000 miles a year. That is possible and a new corvette bought and stored and driven 2000 miles a year should be pristine. Having said that, I think I would start with a compression check to make sure you have a good foundation on which to build. You cannot repair valve train problems electronically. Also, you most likely know this and did it, but no one has mentioned it so I will remind you that to set timing on that car you need to disconnect the wire on the drivers side of the distributer, Absent that you will not get a good idle. 8* Before is correct on my car and likely on yours and you probably know this but again not mentioned. The correct timing setting is on the red table, drivers side by the radiator. Good luck and keep posting.

 

Man, I've been fighting this C4 for a long time! Sorry for no updates & I do appreciate all the help/ideas.
MONTHS & money resulted in me finally giving up on the entire TPI itself. Car now has a freakin carb & runs great. Kind of embarrassed it went that far without finding the issue until the teardown autopsy, but I found the issue. The cold start injector was randomly leaking. I totally missed that as it was shut off by PCM of NC AND the connector was unplugged, so it wasn't on anyone's radar anymore. On the bench, with the whole TPI unit assembled, it would pop open at low air pressure. I used air instead of gas, but at roughly 38-40psi it would crack open. Sometimes wide open, other times just slightly, but it would open. Easy fix now that I know that, but understand how far I went to find that....I get very determined sometimes!

Anyways, i can convert back to the TPI if needed but I'm going to run the carb for now & probably just go with a Holley Sniper over the winter. The plans changed a lot after this ordeal! The cats are very bad now after all that raw fuel going through them so I'm waiting on an exhaust from Pypes & going headers to clean it up under the hood (no emissions here). The originality is out the window now so I have a open slate to play with

Dont know if this saga is any help for anyone else, but just another thing to check with older barn finds.

 

She's ugly under the hood, but spruces up the driveway view a bit!