4.7 stroker idle issues

[strokemanche]

alright guys this thing has me stumped any help appreciated. it is in a 88 comanche so it is a renix system. its a 4.7 as the title says with a crane hmv-272-2 cam. the issue i am having is and cant seem to figure out where it wants to idle. it will start idle fine for a about 30 seconds and then idle down to almost point of stalling idle back up to about 1500-2000 rpm and start the process all over again. now all the sensors are stock parts except the crank sensor which is new. im just not sure where to start

[strokemanche]

alright well yesterday i swapped map sensors with a known good one off my daily driver so i dont believe that is the culprit. next will be the TPS, then IAC

[Cheromaniac]

Your PCM could still be learning its way around the stroker so I suggest you put a few more miles on it and see if the engine settles down before you throw more money on parts.

[strokemanche]

thats what i was attempting to do. but today i found something new. with it running i loosened up my TPS and rotated it to the full limit of travel both ways and it made no difference in running quality. and lately the trans has been acting a lil funny. it wouldnt down shift when i gas it and it upshifts faster than i think it should. no matter how much gas i give it it still shifts at around the 2k rpm range. so im begginig to think its the TPS. not just because of this but before the stroker went it the old motor did the same thing.

[CobraMarty]

What is your idle vacuum?

[strokemanche]

im not sure on intake vacuum. dont have a gauge. ill try and get one soon and check it

[Cheromaniac]

thats what i was attempting to do. but today i found something new. with it running i loosened up my TPS and rotated it to the full limit of travel both ways and it made no difference in running quality. and lately the trans has been acting a lil funny. it wouldnt down shift when i gas it and it upshifts faster than i think it should. no matter how much gas i give it it still shifts at around the 2k rpm range. so im begginig to think its the TPS. not just because of this but before the stroker went it the old motor did the same thing.

Measure the TPS output voltage with ignition on, engine off, by backprobing the middle wire of the three. Begin with the throttle closed and slowly open it manually until it's fully open. The voltage should sweep smoothly from ~0.7-0.8v closed to ~4.1-4.2v fully open. Any spikes or troughs indicate a bad TPS.

[strokemanche]

im gonna test the TPS tomorrow and possibly adjust it if needed. other than the TPS or IAC i cant think of anything else that would cause it to idle/run like this

[atias]

it can be fuel starvation (idle surge) or maybe overly rich, what injectors are you running ? , and did you checked the fuel pressure ? .
how the sparkplugs look like ? clean or fouled ? ,try increasing you fuel pressure just to see if the problem goes away.
also it can be a bad O2 sensor the ecu is trying to adjust the fuel trim with incorrect values, try disconnecting the O2 and see if the problem goes away(it will make the ecu run in open loop)

[strokemanche]

well tested the TPS today and i do believe its bad. when i checked input voltage with it plugged in it was only about 1.07v. so i unplugged it and checked with it unplugged and had 4.96v at the harness. I then checked resistance between terminal A and B and had about 15ohms so my TPS is shorted. buying one tomorrow and putting it on and hoping this fixes the problem.

[strokemanche]

Well guys I'm back. Changed the tps this morning and did the adjustment. With lose to the same results. It still has the same idle and when increasing rpm slowly it makes it to about 2k and starts sputtering and back firing like timing is off. But then I unhooked the vacuum to MAP sensor and plugged it off. With is like this it will increase rpm all the way up but will not idle but for a sec or two. Any ideas?

[Cheromaniac]

when increasing rpm slowly it makes it to about 2k and starts sputtering and back firing like timing is off.

Either your distributor or your timing set could have been installed one tooth off. That would be enough to make the engine run like crap.

[cruiser54]

Start with this:

http://www.cherokeeforum.com/f51/cruise ... ps-153657/

Since you've got a new engine in there and possibly missed hooking up a ground or 2 at the dipstick tube stud, or the block has lots of paint on it, review Post 1.

Post 13 Covers Renix distributor indexing..

Post 8 covers proper TPS procedures. Don't forget to do the sensor ground test outlined in there beforehand.

Post 2 covers the C101 connector. Read it and see why it's so important.