Sorry for the incoming wall of text, but I try to be as detailed as possible when troubleshooting so here goes. I have recently replaced my exhaust from the headers back, (planning on doing a write up on my longtube pacesetter installation that at some point, the how to we currently have is for 4x2, mine is 4x4, MUCH more complicated) and as the title suggests, my engine idle now does some unusual things:

-on cold start, the engine turns over and runs fine, for about 10-15 seconds
-at this point, the idle begins to sound as though the pulses begin piling on top of each other, leading to what sounds like a gallop in the idle. very similar to an aggressive cam lope
-if left to idle, it eventually evens out
-a quick tap on the accelerator also evens it out, and it does not "lope" again until the next cold start
-occasionally, the idle will rev high, then back low, but not with any regularity or predictability

Additionally:

-immediately following cold start, when the accelerator is depressed a tiny bit, say the weight of my big toe, the engine bogs and sounds as though it will die. it has yet to actually quit on me.
-if i depress the accelerator further, or in a quick burst, it sounds and behaves "normally".
-this continues for 3-4 cycles of accelerate/brake through normal driving.
-after this "break in" period, throttle response all at once becomes more regular, almost to "normal" (normal in quotes, as I am almost certain the plenum is blown due to showing many of the trademark signs prior to my exhaust modification, e.g. absolutely no ***** in overdrive, slight oil burn, sometimes engine sounds slappy with reduced power, etc. )

Items I have replaced/modifications prior to the exhaust:

-TPS
-ECT
-ICV
-EGR is currently plugged (there is no EGR port on the pacesetters)
-o2 sensor
-plugs,wires,distributor, coil

Between parts I reset the ECM by unplugging battery for 30min to an hour, and after finishing the exhaust i left it unplugged overnight. Could it be that the plugged EGR is messing with things? This to me seems most likely, as it only has issues when cold right at start up and after a short time smooths itself out. My truck has yet to throw any codes, though even when my distributor cap was bad and it was misfiring bad enough to foul the cat so bad it blew it out, I also got no codes, so that is less than reliable. Or could it be related to further deterioration of the plenum? If that's the case, why would it only occur when cold? Any help with this would be much appreciated.

 

EGR isn't doing anything at cold start, so, that's likely not the problem.

What's "ICV"?

Have you cleaned the throttle body?

Probably need to fix the plenum, to eliminate that as a variable.

What year is your truck? What engine/trans?

 

Ah sorry, meant Idle air control, abbreviated it goofy.

I have not removed and cleaned the throttle body itself, though I have sea foamed the system. (edit: i should note that the IAC when i replaced it was jet black with carbon)

Truck is a 94, with the 318 and 46RE.

 

That would be 46RH, unless you did some major changes.

Aftermarket IAC valves suck. I had a random stalling/unstable idle issue on my 96, put in an aftermarket IAC, and made it worse.... but in an old mopar unit I had laying around, and problems went away. You can find them online for less than the pound of flesh the dealer wants.

Make sure you clean the IAC well out REALLY... erm.... well...... Tends to get pretty gunked up in there, and a bad plenum only makes it worse.

 

hmm... the part i ordered was advertised OEM, would you suggest buying private like from ebay? i have seen that summit has them for ~40 or would that not do me any favors?

also my vehicle information tag under the hood shows my transmission as "A518", isn't that different from the RE or RH? These trannys confuse me

 

As long as the person selling is reputable I'd say go for it.

No they are the same except RH is hydraulic (H in the name) and RE is electronic (E in the name)

 

I believe there is a manufacturer with the name "OEM", That doesn't mean it's original equipment manufacturer I thing they named it that to confuse people. Watch what you buy on ebay lot of trickery there if you don't know what you are looking for. Get the mopar "oem" # and look it up from that.

 

And a lot of them just say 'OEM compatible', or something equally as misleading.

 

Ah, seems I may have fallen victim to marketing tricks. I will search the mopar part number and find what I need based on that.