Thread: Rough idle only when in drive

98 GTP - Usual 3.4" setup

Alright, so I have an annoying rough idle. It's been going on for awhile now. It only does it while in Drive. Park/Neutral everything is smooth. Cold or warm doesn't matter, still does it. The car will shutter/rumble/shake almost like it is wanting to stall out but never does. When I come to a complete stop, the rpms will drop to 500-600(not every time) and then it will go back up to around 800 rpms. Now while I am sitting there at a stop, rpms will fluctuate between 600-900(again not every time) while the shuttering is going on. I can give it a little gas and it will smooth out around 1000. Going down the road she runs as smooth as could be. I haven't experienced any noticeable power loss. No check engine light or anything. It doesn't seem to get any worse or any better.

What I've done so far(not particularity to fix this problem)
MAF sensor
Autolite 104's gapped at .55
New plug wires.. think they are delco's
Cleaned out throttle body and replaced gasket
Inspected and sprayed around vacuum lines(seem fine although I may have overlooked)

I should add this problem existed before and after anything I replaced.

Did you check the vacuum "T" under the S/C? That's a common place for a leak. Also, maybe the EGR pipe?

Originally Posted by FordMan77

Did you check the vacuum "T" under the S/C? That's a common place for a leak. Also, maybe the EGR pipe?

Yeah,the lines around that area look brand new. I sprayed it just to be sure, still did nothing. I haven't really checked the EGR. Is there anything in particular to look for? The 2 hoses from the EGR look fine from what I could see. Should I pull it off and give it a look?

A lot of times the tube will crack inbetween the accordian sections or right where it meets the LIM. You could pull it, or at least spray that area and the tube to be sure it's not cracked.

My GT did the exact same thing RPM-wise for quite a while when it had a vacuum leak. Since you're S/C'd my fix wouldn't apply, but the vac leak thing could still be it. Maybe check the line coming from the brake booster.

I cleaned the IAC when I took the tb off and cleaned it. I guess I will pull off the EGR and give it a better look and re clean the IAC just to be sure. It's 2am.. I'll report my findings tomorrow afternoon.

Alright, found the culprit. I didn't take off the EGR but i sprayed around the hoses. Fordman, you were right. Its leaking right where it meets the LIM. Appreciate the help! Now.. where do i find those stove pipe looking hoses? Is it even worth replacing or should I just do an EGR delete?

Not sure where to find the metal hoses. I just replaced my entire EGR w/ one I had laying around from another motor when the valve itself went bad. You could delete it, but it will most likely throw a CEL for it until you can tune it out of the ECU. I think the tubes on my old one are still good, I'd have to check and see how they come off. Never really looked.