landshrk

I just purchased a '91 pickup, 4x4, 4cyl EFI. I moved to Louisville, KY, and since being in the cold weather (below freezing for the last week or so), the idle won't sit still after the engine warms up. It does the normal warm-up thing, chillin around 1800-2000 RPM until the engine's warm, where it drops down to a lower RPM level.

But... And there's always a but... When I'm stopped, in neutral (red light, stop sign, traffic, what have you), and my foot is on the brake, it'll idle from about 800 to around 1100 RPM, constantly bouncing back and forth. When my foot's not on anything, it does the same thing, only between 1300 to 1750 RPM.

I just had a mechanic look at it, and while he had it, I had him winterize the thing, replace the thermostat, clear out the PCM, and replace the fluids. I could well do all this myself, but it's really effing cold, having just come from California, and I don't have any of my tools here, so... Anyway, he said that a tune-up would fix the issue, but after replacing the necessary electronic components, and getting the timing on point, the problem persists.

Any ideas? Maybe someone had this problem before? Any ideas/tips/solutions would be outstanding. Ask any questions you need, I'll do what I can to answer them the best I can.

Thanks guys!

landshrk

Okay, so I looked around, found some links on other forums, read the FAQs, and tried adjusting the idle screw. It's screwed all the way down. Like, ALL THE WAY, and I still have issues. As I adjust it out, the gap between the top and bottom of the surging shrinks (the range is smaller), but the idle get higher and higher, and even with it screwed out 6 or 7 turns, it still surges.

So, I'm guessing it's vacuum-related. I'll get out there tomorrow, see what's up, see if I can fix any leaks I may find, and post again. If you have any other ideas, please feel free to let me know.

Thanks again.

newman

just had the same issue on my 1990 4cyl.

sounds like a vacuum leak, which is exactly what mine was. the rubber boot that connects the intake to the throttle body was cracked 1/2 way around, just never noticed it.

my problem only persisted when i had my foot on the brake, and only sometimes.

check around for vacuum leaks.

abecedarian

most likely, the auxilary air valve on the underside of the throttle body is stuck 'open' or you have a vacuum leak or an issue with the duct from the throttle body to the air cleaner.

Not saying that's the definitive causes of your problem, but it's somewhere to start.

Yotapowa

I agree, deff sounds like a vacuum leak, also check all your vacuum hoses, it might be as easy as a loose hose somewhere that got overlooked.

seisdtaex

iTrader: (1)

I just went through the same problem. Hard old cracked throttle body boot. Do yourself a favor and do the ISR mod. Got to run to work so no time to find the link but you'll find it with a seaech. Good luck!