I've got a '98 360-powered Ram with a 150k thats had an ogoing idle problem for about 2 years now. Basically if left alone to idle for more than a minute or two (especially ifjust cranked) it begins to lope erratically as if its about to stall. The truck has always idled a little rough, but its gotten consistently worse over the years. On a hot summer day I can't even sit at a long red-light before I'm forced to keep one foot on the accelerator in order to get some air to the engine.

I pulled the air cleaner to try to locate the culprit, and even hooked it up to one of those dealership scanners. It appears the IAC starts going berserk if there's no throttle stimulation. My vac gauge indicates around 24in/hg in a good idle, which drops off gradually to as low as 10in/hg along with a high-pitched sucking noise as the IAC plunger starts closing off the idle air port. This causes the lope and way too much gas in the idle mixture. Sitting at a drive-thru with the windows down I can start to smell the richness as the idle begins to screw up.

One would think the solution would be to replace the IAC. I have --twice. It seems to help for a few days then goes back to the same old ****. I'm using an M1 manifold which I checked vigorously for vacuum leaks after installation. It did this even before the new manifold, but it didn't help things either. I've replaced a number of sensors thinking that maybe an input sensor was telling the PCM the adjust the idle based on faulty readings. O2 sensors, spark plugs, wires, ignition coil, you name it I've probably replaced it trying to fix this.

Any suggestions?

 

Sounds like the problem I was having. Dodge replaced everything they could think of and it didn't solve the problem; went to an independent mechanic who ultimately solved the problem: carbon build up. The mechanic ran two cans of OMC engine tuner through the TB. OMC stands for Outboard Marine Corp - Johnson/Evinrude. Basically the stuff is a foaming carb cleaner for 2 and 4 stroke combustion engines. You run the engine to normal temps, pull off the air cleaner and skirt a can or two into the TB while at fast idle. Then you let the stuff sit for six or eights hours. Then start the engine and idle untill all of the white smoke goes away - about 15 minutes. Then get on the highway and go for a nice ride to burn off all of the deposits that loosened up from the cleaning. The stuff will cost you six bucks a can. Might consider using air intake cleaner on the TB and injector cleaner in the tank at the same time. I do all my toys with this once a year... cars, boats, snow blowers, mowers, etc. The problem never came back andreturns my MPG at normal levels.

I hope this helps.

 

not disagreeing, just trying to understand. reckon what the carbon build up was doing to the idle ? causing detonation, preventing valve close ?

 

I never askedthe technical why, probably should have, now you have me wondering.

 

Yes I've used the stuff before. SeaFoam or something like that. Put a can in the tank and seeped one through a vacuum hose until stalled, let it sit, ran the smoke out. Didn't notice anything.

When I installed the M1 I cleaned the TB thoroughly.

 

Probably got to the point that it was screwing with the map sensor readings.Map may be your problem as well. Are you getting rich codes? When you dip down to 10.5 in/hg, the pcm thinks that you are under load (thinks you have your foot on the gas pedal)and throws more fuel in. Since theyou are not actually under load, The butterflies aren't open and you do not have the air to go with the fuel.You can also try to adjust your iac counts thismay help to get idle to stay up. You need to seal off the idle air port at the top of the throttle body then turn the srew on the throttle linkage until your rpm's reach 800. Then unseal the iac port. The idle will shoot up and then creap back down. If you cannot get the idle to 800 just get it as high as you can. There is a fine line between where the rpms will slowly creep up and where they shoot up over a 1000. The lower side of that fine line is what you are looking for. A good scanner (drb, Snap-on, Genysis) will allow you to do this without plugging the iac port.

 

even though it didnt do anything im sure it was still worth while watching your truck smoke out the neighborhood

 

Actually I did the "carbon cleaner"in the shop whenI worked in a dealership service department. Really pissed the techs off.

I'll give the idle RPM adjustment a try. If that doesn't work I guess I'll replace the TPS and MAPS.

Thanks.

 

my 5.9 is doing the same thing. the main reason was the engine compartment getting filled with muddy water. haha! must be an electrical thing....