I have a 1991 3.9l Dodge Dakota, Auto, 4x4 and recently I noticed when I started the truck the engine immediately revs up to 2700-3000 RPM and slowly settled down within 4 or 5 seconds down to the proper "normal" idle. This is a very high idle for this truck and it doesnt sound good when it starts to rev that high. These trucks are known for dry chatter when they start anyhow until lube gets circulated. Ive had a lot of problems with this truck in the recent past. In one situation I tested the TPS(which I believe may be the culprit right now causing this) and it tested with a meter as "OK". The truck Revs high when its started whether its a cold start or a hot start.

I have replaced the following in the past month or so:
* Idle Air/Speed Control actuator and motor(set the idle as recommended per the Haynes manual and AllData)
**THIS TRUCK DOES NOT HAVE AN AIC THAT GOES INTO THE THROTTLE BODY. ATTACHED IS A PICTURE OF WHAT IT LOOKS LIKE**
* Coil, Plugs, Wires, Pickup, Entire Distributor, ASD relays, Clutch Fan relay
* Water pump/hoses/thermostat
* Coolant temp sensor
* Cleaned the Throttle body
* Replaced the fuel filter and have ran at least 5 full tanks with Sea Foam treatment threw the truck
* Checked throttle body gaskets(appear to be ok)
* Checked for vacuum leaks, none found.
* EGR is bad and has been disconnected and the vacuum line serving it plugged.

Any input would be appreciated, Thanks in advance!

 

Does it do the same thing if you unplug the "throttle kicker" IAC on the throttle body?

If so, it's most likely a vacuum leak. If not, it's most likely the throttle kicker.

RwP

 

The IAC I just put in my 94 3.9 came with instructions about making sure the plunger was not sticking out longer than the one I removed and instructions for how to shorten it if it did. Apparently it could do internal damage to the TB if it were too long to start. The PCM has to get used to the new one, the instructions recommended I drive at 40mph for a while to get it dialed in. Maybe if yours was too long when you installed it, it is telling the PCM it needs more gas because it can't open up or retract enough to open that gap it plugs?
The TPS is cheap change it. Having an EGR might help. Is the butterfly sticking open at all?
Otherwise see about having a shop put it on the machine to find any anomaly's.

 

you know i went through this with my jeep when using aftermarket parts.. changed tps or IAC(idle control) it started and reved 2500~rpms ended up both aftermarket parts send a higher signal to the computer, i put original failed parts back in and it idled and ran normal, till it hit the dead spot on tps and MIL came back on tried 2 aftermarket sensors off a buddies jeep, known good, did same thing.. i was stumped.. ordered both from stealership, Jeep runs like a champ.. im still confused on this one but hey ...

Anyway have you tried pulling codes with key on/off/on/off/on ... and watching check engine flash for codes.?

my 92 4x4 had a faulty TPS and never threw a code till after i changed the AIC again i got both tps and AIC from the stealership... cause the aftermarket failed within a week, lesson learned.. twice lol