Hi, I recently bought a 1998 dodge 1500 4x4 5.9 v8 with some problems. It runs fine, but its been idling very high, it used to be 1500 rpm, then 2000, now its idling at 3,000 rpm. Thats with the Throttle position sensor plugged in, otherwise its normal at about 750.

Ive tried replacing the throttle position sensor and the idle air control, no change. and now with it unplugged it will cut out randomly for a second, the rpms just drop, then surge back. other than that it runs perfect, but its a huge problem i cant figure out. any help is appreciated, thanks

 

What brand of TPS did you purchase?

 

i bought the oreilly brand, borg warner or BWD.

 

Reason I asked is some cheapo brands of TPSs are bad out of the box. However, I've personally had a BWD TPS, and it worked just fine, so I doubt thats the answer. BWD is usually an OK brand anyway.

Have you tested the wiring harness going to the TPS or the IAC motor? Have you cleaned your TB?

 

probe the back of the tps with a multimeter set to 20v dc with the ignition on and the tps plugged in. put the negative probe in the left wire on the pigtail and the posative in the middle wire. the middle should read 5v. pull the posative probe out and put it in the wire on the right, it should read somewhere around 1v, have another set of hands move the throttle from idle to full throttle and you should see the voltage go from 1ish to 5, but it shouldn't go over 5v. also it should increase smoothly (1.2,1.3,1.4....). if it doesn't then its bad. and i may have the middle wire and the right one (from the driver side) backwards, either way one will read 5v and the other will read 1v. and don't cram the multimeters probes in there too hard, it doesn't take much to make contact.

 

How many miles are on your truck? Others will correct me if I'm wrong, but would the EGR have anything to do with this or you have a vacuum line that's leaking somewhere.

 

Possible vacuum leak or bad map sensor... Stab in the dark...

 

im thinking it has to be electrical, because it idles perfect with the tps disconnected. Ill check the wiring harness tomorrow, ive been busy replacing all the front end bushings, it was getting horrible death wobble at 25mph and up.

 

I wouldn't think it'd be the MAP sensor, that usually kills your truck's idle rather than spiking it when that dies. At least, in my experience anyway. Vacuum leak, though, might do it as well.

Test those harnesses first, and then if necessary, move on to vacuum leaks.

 

fixed it, the connector at the ecu had some corrosion, and i think the jet pcm chip was broken as well, the casing around it came apart. cleaned up the connection, now its running great again. thanks for the help guys