My '88 B150 began a strange fluctuating idle thing after I replaced the plugs, wires, cap, and rotor and air filter. It only does this in Park and Neutral. It's almost as if someone was pressing down on the gas pedal slighltly and letting up again. Pressing down, letting up. Its doing small rev ups on its own in park when idling. What is that?

 

Sounds like an issue with your IAC valve.
https://dodgeforum.com/forum/dodge-r...n-the-iac.html

 

An '88 does not have an IAC valve like the MPFI Magnum engines. The ECM controls the Idle via an Idle speed actuator motor.

Maybe the computer needs to relearn your engine. Try disconnecting the battery for 10 minutes to reset the computer. Then drive it, when it's warmed up, drive it like you stole it.
When at full temp, shut it off, restart it and drive normally.

If it still does it, it might be a failing fuel pressure regulator or fuel pump.
--------------------------- the idle actuator motor.
---------------------------, a vacuum leak
or ??????????????????.

 

Wow, how did I miss that.

 

Ok, gents. I have disconnected the battery for an hour and hooked it back up, drove it for a while and here's what I've noticed. This up and down idle thing happens only when the engine is already warmed up. It wont do it on first start. Whe I first start it cold, she purrs like a kitten. But after driving for a few minutes and coming to a stop light, it begins to do it, now even in drive and reverse. Its doing it to the point that if i dont give it gas, it stalls out. However, upon restart, she purrs again and won't start the idle up and down thing for another few minutes when coming to a stop. When driving, I notice nothing unusual. She runs better than ever. And remember, this idle issue arose directly after replacing cap, rotor, wires, plugs, and air filter. I just don't know where to look.

 

What did you set the gap at on the plugs?

 

.035 is what I was told to set them at

 

Take the engine cover back off and make sure you didn't accidentally disconnect a vacuum line somewhere while you were perfoming the tune-up. It's easy to dislodge connections, especially when replacing the plugs and wires. Sometimes rubber vacuum tees and connectors work fine for years, but if you disturb them they fail.

 

all vacuum lines are intact. I just dont get it.

 

When it is loping, is the idle speed actuator motor's pintle moving in and out.

Are there any codes? Do a key dance.