well actually is more like a hemorrhoid >>>
'98D1...been chasing this issue for a while, came on from out of the blue, on a cold start-up the engine immeadiatly revs to about 1800 or more rpm. If you drive the truck for a trip around the block to warm it up, and stop ( put it in park) it wants to idle @ 1000 -1200 rpm,.....shut it off and restart it it has a surging idle that goes from 750 rpm down to barely running and then back up to 750. runs fine otherwise. No CEL , no codes

I try to keep this this tuned up pretty regularly....plugs/wires/spotless clean throttle body/no vac leaks etc etc...

I just ordered an Ultragauge....not here yet so I dont have any good info on the sensor inputs yet..

I have searched forever and once found a suggestion from Higgs B. to turn key on, turn key off, unplug the IAC , key back on, plug in the IAC, start engine......
if I do this the high idle is not there, but the wavering 750 - low idle is there.....

does this sound more like a failing IACV ? OR need of an ecu reset ? OR wtf ?

as always your comments are appreciated .....

 

Any problem with the TPS trigger this high idle mode. Regardless if you fix any TPS issues, you'll need to reset the ECU.

 

Once you have some live data should be able to see codes and if TPS is off or something else, once the cause is fixed an ecm reset is required

Do you have problem filling gas tank some times? Just curious since we are both in salt belt

 

Yeah, once in a while the tank fills " slow", I also had the same issue with the fuel tank pressure sensor failing as you did ( it's unplugged for now...) thanks again for the info on that one !

 

Was it unplugged before or after the high idle?

 

high idle came first...then 3 days later the code for fuel tank pressure sensor....2 days after that it wouldnt run hardly at all....gagging rich choking it self at idle(undriveable)....then i saw your post about unplugging the sensor at the tank.....while it was gagging and barely running I unplugged the sensor and it immeadiately cured itself....except back to the high idle issue...

 

Not familiar with the 98's, but it sounds much like a stepper valve sticking... At least on the 94 model...

 

It is IACV making it idle high but 94 is different computer system, by your description at this time I would get the ecm reset and leave that sensor unplugged till you get a new/ used fuel sending unit, I screwed around so long it killed an 02

 

Where is the fuel tank pressure sensor ? Is it part of the fuel level sending unit in the tank ? I've never heard of this before, so I am interested in case this happens to me ! TIA.

 

Yes part of the fuel pump assembly on ael rovers 97.5 /99.5 d1 that's why our sender is so $$$ compared to early d1