Odd idle problem

At times when I come to a stoplight (1990 MJ ax-15) the truck will idle high. If I tap the throttle it will rev normally then come back down to a normal idle. What could cause this? Throttle body, IAC and TPS are adjusted and clean.

Is the throttle butterfly plate closing all the way every time? the shaft might be sticky, or the spring may be weakened.

I had the same problem in my 87 4.0 - It turned out that the throttle cable was sticking. I lubed the hell out of it and the problem went away.

92DripCherokee said:

Is the throttle butterfly plate closing all the way every time? the shaft might be sticky, or the spring may be weakened.

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Had this problem on my 87. Re-adjusted plate to seat correctly when closed. That ended the problem for me.

Try opening the butterfly by hand, then slowly and gently easing off to simulate normal driving. Mine would stick, unless I let go fast, simulating tapping the throttle. That's how I finally found it.