Cole Peters

Ok guys, I know this is a ridiculously overly-common problem and trust me I have done hours of research before posting this so please don't think this is the first thing I've done trying to fix my issue. Ok, so this is what's going on, like I said I've got a 92 lude with the F22 in it, and the idle likes to surge somewhat frequently between about 1,200 and 2,000 RPM. It does it much more when it is cold outside, like 50 degrees or less. On days that it's 70 plus outside it does it much less. The car has done it ever since I bought it and since then I've done a timing belt job on it, adjusted valve lash, replaced lcv valve, and both the FITV and IAC valves are brand new. It seems to drive fine and runs fine when I hit the gas but as soon as I let off it goes nuts again. I think it's probably one of a few possible things, but any input would be appreciated. I think it could be the EGR valve, Throttle Position Sensor, gasket leaking somewhere (I work at an automotive shop so I have access to a smoke tester, I just need to use the damn thing) air boost valve, but I doubt it (somebody who owned the car before me put a cold air intake on and it does not have a nipple for the air boost valve so the vacuum line is just hanging in the engine bay) O2 Sensor, the car does not currently even have an O2 due to previous owner installing aftermarket exhaust and not putting O2 back in. Throttle body may need cleaning, but again I don't think that's the issue. Or last but not least the bastard of problems, some kid who had the car before me was an idiot, and I'm afraid he adjusted the idle speed to cover up some other problem. 98% of the time the car idles at around 1,400 RPM. When the A/C kicks on it does go down a considerable amount but 1,400 is really high after warmed up. Sometimes it will go down to around 1,000 but very rarely ever idles below that. I think I've covered pretty much all the bases here guys lol, but like I said if anybody has some extra knowledge on this I'd greatly appreciate a tip or two. Thanks

Cole Peters

Also the coolant was bled, and new thermostat installed last winter.

holmesnmanny

If you replaced the iacv and fitv that means you have a vacuum leak.

You need some carb cleaner and gently spray around the intake manifold til the idle changes. When it does, you've found the leak.

Cole Peters

I've been told that smoke testing the intake is more effective so I'll probably go that route. If all goes well this week I'll park it in our shop Friday night and let it get dead cold and test it Saturday afternoon and let you know what I find out.

Cole Peters

One more thing, the A/C seems to smooth out the idle. A couple times on warm days I will be at a stoplight and it'll be surging over and over and then I hear the compressor kick on in it's cycle and the surge stops immediately.

holmesnmanny

Whichever way works best for you. Not a lot of mechanics have a smoke tester.

Cant honestly say why the ac has an effect. I would only be speculating.

snobordboy

Test for leaks, clean your EGR, properly adjust your TPS, put on an O2 sensor, then see how it is doing and if you still need help.

The only thing that will cost you any money is the O2, and it will probably make its worth back in gas savings within 6 months anyways, aside from ensuring that everything is working right.

Cole Peters

Ok, I may end up just replacing the EGR given it's so old and has so many miles on it anyway, and I've thought about the O2, but here's a weird fact, driving the car nice around 55mph I've gotten 43mpg with it more than once. This was during 100mile trips or longer too. I doubt I can squeeze more mpg out of it than that but who knows, it's worth a shot. Also, since it's an aftermarket exhaust with a 4-2-1 header, the bung for the O2 is pretty far back, so I would need an extension for the O2 sensor and I've seen them for sale on ebay, anybody know exactly what to get? I could probably figure it out but maybe somebody else has needed this before and can tell me what they got. Just to check, I'll make sure the throttle cable is adjusted well too, correct me if I'm wrong but it would make sense to me if it was adjusted to where it has no slack, but is not pulling on the butterfly valve. If that's incorrect let me know. One last thing, how do you adjust the TPS? I haven't heard of that yet. Thanks guys