Pretty much a stock 91 L98 Formula that I bought last summer and haven't had time to do much with yet. Anyway, since I bought it, it's had this nasty surging idle problem only when restarted hot. It revs up and down for about a minute or 2, around 1400-400, back and forth, then all of the sudden it's GONE. Then it'll run and idle like "butta". I've been through the IAC and replaced it with a good one, cleaned out the passages the best I could. I wouldn't think it was the IAC though since the problem just goes away, and wouldn't think that an IAC would all of the sudden start working at the nearly the same time, every time. Then I was thinking injectors, but again, why would they only act up on a hot restart? I'm kinda thinking something to do with a possible hot start open loop condition. Any ideas?

 

Check your TPS voltage and maybe clean out your MAF sensor with some MAF cleaner by CRC.

 

TPS voltage is fine, and no MAF, speed density

 

any chance the egr or something else is causing a vac leak?

 

Check for leaking fuel pressure regulator through the vacuum line, and for leaking fuel injectors.

Check for vacuum leaks on the canister purge system.

 

Well I've replace all of the lines in the EVAP system and no change. I don't think the FPR has a vacuum leak since it just goes away all of the sudden. I may have to recheck the vacuum to the EGR, but I don't think it's leaking. Either way, I'm looking for something that will just go away like the flip of a switch after a couple of minutes after restarting hot, or just starting cold. I'm not really certain which functions are controlled differently during a hot restart.

 

oh I meant the EGR valve getting stuck open or at least taking too long to close?
the egr's vac control doesn't seem like it would cause you're problem but no harm in checking

 

I agree with the EGR thing. I had the same problem. It would run great when I was on the throttle, but ever time I came to a stop, it did what yours is doing. I did a datalog and the EGR was opening at very low speeds. I deleted the EGR out of the prom and I has not happened since. The EGR is only suppose to open at higher speeds 55+ I think?

 

from what i can tell at least on mine, the Vac line that goes to the EGR is ported vacuum so I'm guessing its open whenever you're accelerating or cruising but my vac system isn't in the best shape either so I can't say for sure

 

I bought my car after it sat for 8 years. Once I got it running I had so many idle/surging problems. I had vac leaks up the wazooo. I replaced every single vac line and it ran great after that. No surging problems, no idle problems. I put 2000 miles on it that season.

 

I took my egr off and cleaned it as well as the passage going to and from it then checked to make sure the egr wasn't leaking anymore (carbon buildup was holding it open) that seemed to be all i'd needed for my idle problems

i just have a relentless 33 error while i'm driving that seems to have no solution, I made a post about it but no one ever replied