Rough idle when starting.

c101guy

Registered User
90 5speed. When started, rpm's drop off and it wants to stall. If I keep my foot on the throttle at about 1500 rpms and occasionally rev it, she eventually smooths out and then runs fine. Thoughts?
 
90 5speed. When started, rpm's drop off and it wants to stall. If I keep my foot on the throttle at about 1500 rpms and occasionally rev it, she eventually smooths out and then runs fine. Thoughts?
Hot/Cold or doesn't matter?
Large vacuum leak or EGR valve are 1st thoughts.
 
Thanks for the responses.

Cold. Once she warms up a bit and settles down, she restarts and idles. After cool down, it's same stuff, different time.
 
Both my 89, and 90 SC's have a hot soak issue. Hot engine restart after sitting 15-25 minutes. The fuel pump makes a sound like the fuel is aerated. My 90 has the original fuel pump, injectors, and regulator. Been doing it for 20 years. My 89 5spd has a new fuel pump, filter, injectors redone, and flowed. Regulator doesn't leak into the vacuum hose, either. Runs, and idles great, other than the hot start stalling, and roughness. I also hold the revs at about 2,000rpm for a few seconds. The fuel pump also makes the same noise. I've heard it is caused by winter fuel blends. I've tried non ethanol, and added techron. Lately it it seems better. I measured the fuel tank temperature, and it was under 80°. I'm thinking hot fuel at the pump.
 
We posted at the same time. Coolant temp sensor can be measured. Possible vacuum leak at air intake tube, and breather hose, that doesn't affect a warm engine as much. Does your IAC work OK warm?
 
90 5speed. When started, rpm's drop off and it wants to stall. If I keep my foot on the throttle at about 1500 rpms and occasionally rev it, she eventually smooths out and then runs fine. Thoughts?
When I had same issue it was my idle control valve had carbon build up, replaced it and all was well. Not saying that's your issue but they cheap enough to replace easily.
 
Normally I'd agree, but in this case c101guy has to keep RPM's at 1500 or above.
I don't think the IAC is even capable of taking it that high? Their must be other issues
 
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