Idle problems after warm up, RPMs rise when the brakes are pumped. | Ford Explorer Forums - Serious Explorations

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Idle problems after warm up, RPMs rise when the brakes are pumped.


November 24, 2009
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City, State
Year, Model & Trim Level
1998 Sport
So my truck starts up perfect, it idles fine until it warms up and then, when it drops the RPM's down to about 700 it starts oscillating and shudders a bit. This has been bugging the tar out of me. I have noticed that when I pump the breaks the RPMs will rise to 1200'ish and it idles there for a few seconds, then drops back down to 600-700 and starts idling rough/shuddering again.

Is this a brake booster problem? Any ideas?

1998 Ford Explorer Sport (2WD)

Also: I have cleaned IAC and MAF, and changed the air filter... no big difference.

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Which engine?

Do you have the OHV or the SOHC? The SOHC is notorious for intake manifold vacuum leaks that affect the idle speed.

Are any DTCs being set by the PCM?

Pumping the brakes could deplete the vacuum reserve and impact the manifold vacuum which affects the idle.

I suggest that you perform a manifold vacuum test for idle fluctuations.

I suggest that you try performing the Idle adjustment procedure

It is an OHV.

Seems like it does fine, until it warms up.. hm.

I checked Brake Booster line, doesn't seem like its leaking.

I've gone around the Intake Manifold with an unlit propane torch, couldn't find anything.

My ears might be deceiving me, but I'm pretty sure i'm hearing a sucking noise from somewhere.. egh.

Also: No CEL, it will come on every now and then... stay on a day, then go off. Went to Autozone and they said they'd only do it when CEL is on. Guess I'll have to catch it when it pops on.

Edit: How much do you think it'd cost to have a mechanic smoke it out?