Hi everyone - new to the forum. Glad to be here. Please take time to weigh in on this issue as I am out of easy answers.

Couple weeks ago I stumbled onto a 92 dakota 3.9 magnum extended cab truck....with 98kmiles on it...owned by some older folks...bought it...paid only a grand for it. Truck is in pretty much immaculate shape. The owner said it had a small engine noise (before I bought it) but I looked at it and chalked that up to a bad water pump.

I changed the water pump out which made the engine noise disappear - did a complete tune up on the motor which consisted of:
-clean and inspect IAC (works now)
-shake PCV valve (works)
-replace cap, rotor, and spark plug wires
-replace spark plugs
-clean and inspect crank case ventilator (don't know exactly what it's called on this truck)
-cleaned throttle body
-replaced air filter
-replaced egr valve and vacuum controller

I have inspected all the vacuum hoses that lead to and from the engine and all 'appear' to be fine...in addition...I sprayed carb cleaner all over each and every vacuum point to see if I could get the motor to stumble...no stumble. Throttle body bolts are tight and all the intake manifold bolts are tight. No hissing.

All cylinders register right around 150lbs EXCEPT #4. #4 cylinder is 120lbs.

I have NOT taken off the throttle position sensor and looked at it or replaced it. I have not taken off the map sensor and looked at it either. I have not looked at the PCV grommet or the CCV grommet...but...the motor doesn't stumble when I spray them either. There is no check engine light on (I don't even know if this model has one).

I don't have a borescope so I can't look at the piston on number 4 or the valves for that matter.

The engine will run like a top when you are the accelerator...but when you stop at a light and the truck is in gear...it will 'lope' real hard. Shakes the whole truck. I don't think this is electrical. No light shows at night.

Can someone recommend something I might have overlooked?

Thanks folks!
Chris

 

The IAC is the typical problem when coming to idle problems. Are you sure it is working? A slow moving IAC still will cause you problems. It is best to replace it.

 

Well...I can hear it working. I know it works. Slow moving IAC....hmmmmm.....just chewing on that concept.

If it's slow.....it's being slow the ENTIRE time I sit at any given red light and waiting for it to turn green.

Based on what I hear when I'm under the hood....it closes pretty fast. I don't really want to buy an IAC to figure that out....although I could just go to advance ask to hold one....touch it....feel it....love it. That might give me an idea.

Thanks for the input.

 

I examined a new IAC today....mine is good.

 

Willing to bet its the TPS. It triggers a code, but not the check engine light. I had the exact same symptoms. While coming to a stop, I would watch the ammeter. I would see it drop and feel the whole truck shake, then it would come back up and seem alright. Does the engine rpm's fluctuate much at a steady throttle?

 

ok. Have a 1996 Dakota v6 3.9L, manual 5 speed, 2wd. IAC valve, plugs & plug wires, distrib and rotor all new. Idle is between 650 & 700 after warm up. Thermostat replaced also. Problem is idle is rough enough to shake the truck ! Acceleration is fine, no bog, not rough ... smooth as can be. Only during idle does this problem exists. I don't have the tools to do compression check, but assume that totally clean burning plugs with no evidence of oil means my compression should be ok..? .. I'vr also cleaned the throttle body, added injecter cleaner to the fuel... could this be the TPS causing the problem ? I see it was for 1994 models ... but what about 1996 ? Oh ! Also ... have a "stone in a can" rattle... seems to come from the front of the engine... checked the pullys and they are fine ... water pump "looks" new , doesnt leak ... what do you think ... water pump or the dreaded timing chain slap ? Could this also cause the rough idle ? Thanks for any input !

 

Sounds like a problem I ran into last week, turned out being the brake power booster check valve was leaking around the grommet.