I Need Help!!! Car Has Been Pissing Me Off For Months!!

[92GNZ28]

I bought my '87 GN about a year ago and the motor had a rod knock. I knew this already and had a new motor built. It has Champion Irons, PT-52, PTE Front Mount, Delphi 50's inj., Accufab 65mm TB, Poston almost stock cam, Poston Headers, Poston 93 chip for the 50's inj, Pat's 10" 3200 L/U converter..

The problem is the idle. This car won't idle worth a sh*t. Hunts and surges, acts like a vaccuum leak, but trust me I have done everything to find one, work at a dealership and have used the smoke machine numerous times, replaced ALL hoses, IAC sensor, etc. The car has never had anywhere close to 17 in. of vacuum @ idle. The most I can get is 10 in park, in drive drops even lower. Thought I found the problem a couple days ago, thintake manifold gasket seemed to be leaking. Replaced it and still hunts all over the place, replaced EGR valve, no change. I can't get the IAC to drop down to 15-20 counts with the idle srew in or out all the way. Unplugged the IAC and seems to run a little better. Also didn't throw a Check engine light while the sensor was disconnected. Car runs fine at anything over idle. Will surge anometimes stall coming to a stop.. . . I'm at my wit's end here, car is making me lose my mind!!! Only other thing I can maybe hear is a slight exhaust ticking from pass. header somewhere. HELP ME PLEASE!!

 

[soundguy]

you may have a bad MAF. with it plugged in, tap on it with a screwdriver handle. The car should studder. Also unplug it, the car should change in idle too. If either of these proves true, you got a bad MAF.

 

[VadersV6]

I always had a bad idle issue. It barely ran when I got it, but now it idles pretty well. Ive done just about everything you can think of. When you think you've done it all, there is still alot left.
Is the crank sensor tight (not loose and wobbling around)? Is it adjusted? (the gap on both sides of the interrupter ring) Mine was loose.
Is the cam sensor adjusted? Try installing a new one if you set this one and nothing improves.
Do an ohm check on all your plug wires.
Ohm check the coil posts. (front to back on each coil..should be around 12kohms)
Is the EGR working? It should be off at idle. If its open at idle, the engine will run terribly. First, pop the EGR solenoid filter cover off and see how dirty the filter is.
With the engine idling, reach under the frame of the EGR valve, and pull up on the diaphragm. It should start stumbling really bad. If its already pulled up from vacuum, (which it shouldnt be) move onto the solenoid. To check it...with it idling, pull the EGR hose off, and feel for vacuum. There shouldnt be any at idle. If there is, the solenoid is bad.
With the hose off, pull up on the diaphragm again, plug the vacuum barb on the valve with your finger. Let off of the diaphragm and see if it drops. It shouldnt. If its very slow to drop, its fine. If it drops fast, the diaphragm is torn.
Get a screwdriver and pop the solenoid off for the charcoal canister. Check the O-ring to see if its still in good condition and sealing. Put a little grease on it when you re-assemble it. Last friday, I pulled that solenoid off and put 12 volts to it with a power supply. I blew in it to see if it was sealing, and cycled the power on and off to make sure the solenoid was moving, and sealing right. It wasnt. Sometimes it would seal and other times it would still leak air. I poured some light weight oil in there, blew it out with a blow gun and went back and kept cycling it while blowing in it. It works fine now. I also put in a new o-ring, and the idle has improved alot.
Another thing that really helped the idle, was opening the gap on my plugs wider. I went to .040, and it works fine. No spark blow out, and its amazing how much better it idles.
Check all those little one way valves that run to the charcoal canister and EGR, and the one by the firewall. Check for leaks by blowing in both sides. They should only flow in 1 direction. You dont want boost going to the EGR and canister.
Check the cruise control diaphragm the same way you checked the EGR, for leaks.
Listen to all the injectors with a mechanics stethoscope. The ticking frequency should obviously be the same with all of them.
Is the PCV valve working properly?
Are the O2 crosscounts moving really slow? If so, replace the O2 sensor. I dont run leaded fuel, so I run a bosch O2 sensor, which was way more active than the delco one.
Replace the MAF.
After all this stuff, move on to tuning it. Its also important to check for corrosion with in every connector you can reach.
I was convinced I had no exhaust leaks. But further examination exposed a cracked drivers side header. I fixed that, and then found the collector gasket where the headers mate to the turbo was blown out. I had so much backpressure that the copper gasket had literally been stretched and pushed out of the flange. The flange wasnt warped at all.
Naturally, check the ground connections on the back of the passenger side head. make sure none of those wires are frayed or damaged, and make sure that bolt is tight.
You shouldnt just stop once you find the issue. Continue to check and fix, because if you dont, your car wont run good for long. The next thing will get so bad that you're back at square 1 again.

 

[92GNZ28]

Thanks for the replies. I will try some of these suggestions tomm. and let you know.

 

[Alaskabuick]

good info

Nice bit of info!

I always had a bad idle issue. It barely ran when I got it, but now it idles pretty well. Ive done just about everything you can think of. When you think you've done it all, there is still alot left.
Is the crank sensor tight (not loose and wobbling around)? Is it adjusted? (the gap on both sides of the interrupter ring) Mine was loose.
Is the cam sensor adjusted? Try installing a new one if you set this one and nothing improves.
Do an ohm check on all your plug wires.
Ohm check the coil posts. (front to back on each coil..should be around 12kohms)
Is the EGR working? It should be off at idle. If its open at idle, the engine will run terribly. First, pop the EGR solenoid filter cover off and see how dirty the filter is.
With the engine idling, reach under the frame of the EGR valve, and pull up on the diaphragm. It should start stumbling really bad. If its already pulled up from vacuum, (which it shouldnt be) move onto the solenoid. To check it...with it idling, pull the EGR hose off, and feel for vacuum. There shouldnt be any at idle. If there is, the solenoid is bad.
With the hose off, pull up on the diaphragm again, plug the vacuum barb on the valve with your finger. Let off of the diaphragm and see if it drops. It shouldnt. If its very slow to drop, its fine. If it drops fast, the diaphragm is torn.
Get a screwdriver and pop the solenoid off for the charcoal canister. Check the O-ring to see if its still in good condition and sealing. Put a little grease on it when you re-assemble it. Last friday, I pulled that solenoid off and put 12 volts to it with a power supply. I blew in it to see if it was sealing, and cycled the power on and off to make sure the solenoid was moving, and sealing right. It wasnt. Sometimes it would seal and other times it would still leak air. I poured some light weight oil in there, blew it out with a blow gun and went back and kept cycling it while blowing in it. It works fine now. I also put in a new o-ring, and the idle has improved alot.
Another thing that really helped the idle, was opening the gap on my plugs wider. I went to .040, and it works fine. No spark blow out, and its amazing how much better it idles.
Check all those little one way valves that run to the charcoal canister and EGR, and the one by the firewall. Check for leaks by blowing in both sides. They should only flow in 1 direction. You dont want boost going to the EGR and canister.
Check the cruise control diaphragm the same way you checked the EGR, for leaks.
Listen to all the injectors with a mechanics stethoscope. The ticking frequency should obviously be the same with all of them.
Is the PCV valve working properly?
Are the O2 crosscounts moving really slow? If so, replace the O2 sensor. I dont run leaded fuel, so I run a bosch O2 sensor, which was way more active than the delco one.
Replace the MAF.
After all this stuff, move on to tuning it. Its also important to check for corrosion with in every connector you can reach.
I was convinced I had no exhaust leaks. But further examination exposed a cracked drivers side header. I fixed that, and then found the collector gasket where the headers mate to the turbo was blown out. I had so much backpressure that the copper gasket had literally been stretched and pushed out of the flange. The flange wasnt warped at all.
Naturally, check the ground connections on the back of the passenger side head. make sure none of those wires are frayed or damaged, and make sure that bolt is tight.
You shouldnt just stop once you find the issue. Continue to check and fix, because if you dont, your car wont run good for long. The next thing will get so bad that you're back at square 1 again.