Erratic RPM's

[1gr869]

I ran a bottle of fuel injection cleaner through my GTP and ever since the RPM's race up and down. Sometimes it even stalls. I've replaced the idle control sensor, throttle position sensor, and fuel filter. The car also idles about 300rpms faster than it should. At idle, it runs 1000. At 55mph it runs 2000. I also noticed a drop in MPG. I haven't messed with the EGR valve yet and I'm not finding any vacuum leaks.

Would the mass airflow sensor cause this?

[richtazz]

I'll assume you're speaking of the 95 GTP in your profile. The 3.4x DOHC is infamous for intake leaks (among MANY other problems) that only develop after the engine heats up. The symptoms you describe are classic of this issue.

[rockford0303]

I was thinking the same intake leak!

[1gr869]

Okay, I replaced both the upper and lower intake gaskets and the RPM's still race up and down. This happens when the car gets up to operating temperature. When cold, it idles fine. I have an identical GTP (same year, same engine) so have swapped a few parts to try different things. My other GTP runs perfectly and has only 56k miles on it.

Here's what I've done so far...

Swapped mass air flow sensor
New fuel filter
New upper and lower intake gaskets
New throttle position sensor
New EGR valve
New idle control sensor
New fuel injector o-rings

Could it be the fuel pressure regulator?

It sucks when you get it to operating temp and you're sitting at a stoplight and the rpm's are racing up and down.

I should also mention that I'm getting 12mpg on the highway and when I pull in the garage and shut the door, I smell gas. No leaks on the floor or anything. Also, I've checked all vacuum lines and there are no leaks.

This thing is driving me nuts!