Rough Idle issue

CADsortaGUY

Lifer
Oct 19, 2001
25,162
1
76
www.ShawCAD.com
Lately, I've noticed some rough idle in my '98 T&C (3.3 Flex)

I have an autoTap to check the codes but all that comes up is the generic "idle" code. So I've just cleared it and it goes away for a while but then comes back. Is it worth the $100 to buy the enhanced codes for Chryslers?

The history of this issue goes back to a #2 misfire code about a year ago which was "solved" by new plugs and wires. It ran great up until about a month ago when the rough idle started.
I've checked the O2 sensors and they seem to be working(can see the mV reading on the AutoTap) so it shouldn't be the sensors. I also checked the Idle air control valve by pulling vac hoses at idle and that seems to check out also. So i figured it could be my injectors since I do run E85 so I switched to reg 87 (no ethanol instead of the 89 which has 10%) and it's run a bit better but still a rough idle. I've run injector cleaner and fuel sys cleaner through it too.

Any thoughts?

Oh, and I forgot to mention that my idle seems a bit high while in park/nuetral. It's at around 1750rpm but putting it in drive it drops down to aroun 1K. From what I can remember normal park/nuetral idle was at around 1200-1300 and then 900-1000 in drive. Also, the idle in park/nuetral alternates every once in a while. it'll go to 1800 then down to 1500-1600 for 15 seconds or so then back up.
 

BaDave

Member
Aug 17, 2006
29
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0
Just for the sake of trying, tap on the idle speed motor and tps. If the idle changes while you are tapping on either one i would guess that is the problem.Also check for any vacume leaks.
 

CADsortaGUY

Lifer
Oct 19, 2001
25,162
1
76
www.ShawCAD.com
Originally posted by: BaDave
Just for the sake of trying, tap on the idle speed motor and tps. If the idle changes while you are tapping on either one i would guess that is the problem.Also check for any vacume leaks.

Yep, I did all that. No dice.

However, I did a bunch of looking around online for the error code(rough idle) and the guy had almost exactly the same symptoms as I did but he had a 3.5L Intrepid. His fix was the intake manifold gasket.
So I've already purchased the gasket kit and have begun removing the top side. I'm about to pop off the upper manifold plenum so I'll know shortly if it was worth the hour worth of topside disassembly.