Rough Cold Idle

Recently, my 1991 NA started idling rough when cold. After a few minutes, the idle is normal. I installed a new MAF last month and disconnected the battery to reset the ECU. At that time, the idle was normal. The idle is acting as if the car is running too rich. Any ideas? Jeff

Idle speed control valve (ISCV) would be first on my list. I had issues with mine that caused the car to idle very low (~400 rpm) when cold. Check for the correct resistance across the pins and for any debris inside the valve (my issue was the latter).

Thank you for your quick response. I try this when I get home. I will let you know what happens.

Is it revving high or low when cold?

No, it acts as if it is going to stall.

The engine acts like it is loading up. I drove a formula Mazda last year. If you did not keep up the RPMs to the optimal idle level the engine would load up (run rich). This is how the idle is when cold. When I increase the RPMs the engine runs smooth until I allow the engine to idle.

The problem was the idle control module on the intake manifold. Boy, was it dirty. The cold idle was fine after cleaning with carb cleaner and a bottle brush.

:triumphant: Nice work sorting it out!

Thanks to you Moerdogg.

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