I've been working on my 86 auto, on and off for about 2 months now. Here is the scoop. When I go to crank it for the first time, I will crank on the first turn and run good for about 2 seconds and then try and stall. If I give it a little throttle it will pop in the TB and run good until I let off the throttle. Then it wants to stall again. After about 1 minute of run time (engine temp approx 100*-115*) it will run with out throttle and surge up and down. When it surges down I here a hissing sound around the EGR solenoid/TB area. Then it goes back up to normal idle and no hissing noise. It does this (surgeing) until the engine temp reaches 140* or so, and goes into closed loop. After it's in closed loop it runs good (no surging). The exhaust fumes are still very rich (open and closed loop) so much that after I shut it off you can still smell the exhaust 20 min. later when walking by. The car shakes a little bit when at idle and my RPM guage on the dash says 88 all the time so I'm going by ear on the RPM's. On a drive it runs pretty well and responsive but when I come to a stop the RPM are noticably high and after a few seconds they come down. It cranks instantly when warm and idles fine.

The ECM chip (I was told by previous owner) is not stock
I have 24 lbs injectors
EGR pipe delete

-These are things I have done:
-Cleaned IAC and TB.... TPS @.54v closed/ 4.0 WOT and set minimal idle using proper steps
-Coolant temp @ 180
-Heated O2 sensor
-No Codes shown
-Timing @ 6* BTDC
-Field test mode: Light blinks one time per second. When giving initial throttle light stays on for 2 sec. then back to one per sec.
-Used propane and WD-40 around for vacuum leak detection an nothing
-Fuel pressure 43 psi key on and 41 psi idle with stock FPR, leak down after shut off is very slow
-new plugs (have a black/gray insulator and white tip and smell like gas)
-PVC valve rattles when shook
-Air filter new
-oil smells a little like gas
-all 8 plug wire have spark and test o.k with ohm meter

I have probably left out a few things I did, I've done just about everything I can think of without a scanner.
Are there any suggestions?

 

Hissing noise sounds like you do have a vac. leak, believe me they can be hard as hell to find! When you cleaned the IAC, did you move the pintel? if you did you need to re-set the IAC, then you'll have to adjust the minimum airflow and adjust the TPS voltage. BTW, when you cleaned the throttle-you probably got an after market gasket(s) most after markets come with 2 gaskets-but only one is right.NOT knowing what chip is in there really would bother me!You said the fuel pressure
bleeds down slow-how far down? Also, you removed the EGR pipe-did you remove the EGR? if not, pull the vac hose and plug it, see if that helps. Good Luck

 

Knew you'd chime in with some advise. The hissing noise is only audible when the engine wants to stall (say 350-400 RPM). I tried with the propane an can't find it, but if I take the accordian off the TB and spray in there I hear an incease in RPM (but it should). I followed the proper steps when cleaning the IAC (by the FSM) and also looked at Vaders website for more. The TB gasket was replaced at this time with Felpro. Yes, the unknow chip bothers me also, could make all the difference (I haven't looked but I think its a Hypertech). The EGR pipe was removed by previous owner and the EGR is still in place and hooked up to vacuum and the solenoid, I have also taken the vacuum off the EGR and put my finger over it and nothing. Thanks

 

When you cleaned the IAC did you put in a new gasket? if not spray WD40 around it while ideling. You've got to locate that hissing sound, and what are you spraying into the throttle body WD40? if so, try spraying around the throttle body area including shaft.

 

No, I used the old gasket. I checked at a few auto parts stores and they told me they don't sell the gasket. So, from what I figure I will have to get a new IAC just for the gasket. I used the propane in and around the TB all over the place. The only change was when I used it directly in the TB butterflys.

 

Think I'd be tempted to pull that IAC again and put some sealer on that old gasket-if you didn't. You might also take your WD40 and spray it pretty good where the throttle shaft is-on the outside. I know it's a hassle finding those damn vac leaks-and I and others have had to check more than once to find them.

Read 87 rag the last page of his post.

 

Alright, I took the TB off again and cleaned the clean TB and the clean IAC mount. I went ahead and wasted my money on a new IAC sensor and gasket and just replaced it. I will leave it disconnected and set minimal idle and check TPS tomorrow. I have tried the vacuum leak tricks once and I will try it again as well. If I can get it to idle right I still have to fix the rich smell.

 

I just ground termal A and B and waited for 1 minute and disconnected the IAC. I know the engine should be warm when working on theses procedures but my problem is when cold. I adjusted the minimal idle and checked my TPS again and it was at .64v probabaly due to taking the TB off so down to .54v. I checked for leaks one more time for about 10 min and can't find it. I need to purchase a vacuum guage and start checking all vacuums. After all this it runs the same. I guess no one has a suggestion that I haven't tried yet, so a scan will be next. Thought some techs would shed some light for me but I guess not. Thanks Rick for your suggestions, I guess I should have just pm'd you.

 

Well, I just went out and washed the vette. Now maybe it will idle correctly and not burn rich.

 

Heck - Somebody's got to throw out the dumb stuff. Of cource you checked the brake booster and related hoses for leaks. Not much else to offer right now. It does sound to lean.

 

Yes pcolt94, I did check the brake booster vacuum. I took it for a drive just a minute ago and once it gets warm it runs pretty smooth. No surging or missing. It seemed it was a little low on power when going from stop to WOT, but I've been driving the 95 some lately. It still does the same when cranking cold and until it goes into closed loop it run like crap.

 

You might try a stethoscope or listening device, hose etc to localize the hissing sound. Maybe if you can find it when its cold it may solve the puzzle.

 

I had tried that at one time and didn't come up with anything but also had my 18m old son running everywhere, so it made it hard to stay with it. I've been thinking about the "mystery chip" thats in my ECM. I replaced the injectors because the ones in it were unknown lbs and one read 8 ohms, but it runs the same as it did before. My father has a 88 and 89 ECMs and I thought about just switching one of them out and see if there is a difference. This could solve my problem and again maybe not, but is worth a try since they will be free.

 

Sounds identical to the problem on my 86E!

Basically runs lean and lousy until closed loop. Then it settles down, yet still runs a touch rough. WD, H2O and propane leak checks are negative. Noticed problem is growing worse.

 

Yeah it's a bugger.

 

Could it be a bad (temp) sensor?

 

Sounds like a timing issue to me. I'd double check to make sure that the Balancer hasn't slipped or that the distributor isn't back a tooth. You'll need something to tell you when #1 is at TDC, but I'd crank it to that position and see where the marks are on the balancer and where the rotor is pointing on the distributor. You might also try loosening the adjustment bolt and then turn the distributor while it's running. My guess would be to advance it, but if retarding or advancing it gets it right, I think you'll stumble across the solution.

 

SunCr, what caught you eye in my first post? This is very likely. I had the distributor bolt loose and turned the distributor to set my timing. It runs best at 6*... any retard and it stumbles. The car also shakes when idling. I was wondering about the balancer doing that. While looking at the timing teeth and the balancer when it surges the timing advances a little until the RPMs come back up (ECM).

 

Timing should move if the RPMs ramp up - there is a little bit of advance built into the module - even with bypass disconnected. That will get you home if the ECM side conks out on the highway.

Your symptoms caught my eye because I've been off a tooth stabbing the distributor back into the hole and had similar symptoms. I finally made a small mark on the intake with my dremmel so I don't have to go through that headache a second time.

I would fabricate something to tell you when #1 has reached TDC or buy/borrow the tool from Autozone. Hand crank it to #1 and see where the rotor is pointing and where the timing mark is on the Balancer.

Assuming it's all lined up, and rereading your initial post, probably not bad idea to try it with MAF disconnected. If it's reading too much or too little air, the fixed values built into the ECM should get it to idle right. If so, the MAF is bad.

 

Thanks SunCr, I haven't worked on the vette much lately due to running out of ideas. The distrubitor could be a tooth off. Before I changed the intake manifold gasket a few months back it ran the same way and the distrubitor was installed the same as it was taken out. I had a little difficulty with the oil pump slot but went in the same. I am going to get a vacuum guage and compression guage and check all, as well as hand turning to #1 TDC. If anyone else has any suggestions I'm all .