surging at idle

[mad_psi-shelby]

hey guys My cars been running great for awhile now, all of the sudden.....when it idles it surge's from 700rpm to 1200rpm and when im driving, I push in the clutch and it sounds like the motors not firing at all then it stumbles around 500rpm then picks up to 700 and surges.....the wires to my 02 sensor are kind of melted im going to fix all of those today and see if it helps. All vac lines are new and intact. Any ideas?? thanks guys

[spudwiser67]

sounds like the tps or the iac may be giving you shit.

[turbokid]

Ya sounds like you have a surge through your electrical system sending mixed signals to your sensors on your tb creating this condition.
And/or a sensor going bad.
Replace the melted o2 and then see if that makes a difference.
Q

[mad_psi-shelby]

is there any way to test the iac and the tps? I put a new iac in about 8 months ago, it was a holley brand sensor and it also was a different shape than the one that came out.........i went back to autozone to check the sensor and the holley one kept coming up for the right part....so I left it in. Id love to check these tb sensors. thanks alot guys

[NAJ]

Did you repair the O2 wiring yet?
That should be priority 1.
The ASD relay supplies 12 volts to the O2 heater circuit as well as the + coil, injectors, fuel pump and an alternator feed.
If the power feed is shorted to another line it will play havoc on your electrical system or may induce stray voltage that the controller is "trying" to read.

Once that is corrected if the problem is still present bring the vehicle to "base" idle without AIS control.
If the surge problem is still present it is not the AIS or control of the AIS creating the problem.
TPS can be checked by "backprobing" the signal and signal return line in the connector with it being plugged in to the TPS,with a digital voltmeter and reading output voltage.
Key on/engine off closed throttle voltage will be anywhere from .40-.90 volts, the controller uses this as its "target TPS voltage" at closed throttle and references throttle position from this base reading.
Anything above 3.50 volts is read as WOT.
With the voltmeter connected slowly "sweep" the TPS, voltage should climb consistantly with throttle opening.
You will be looking for voltage drop off or spikes.

[mad_psi-shelby]

ok guys thank you!....but no i havent touched the o2 wires yet its my bday today so We got stuff goin around the house.....but later today im going to fix the o2 wires and check the timing. Where should the dist timing be on 91 octane with 14psi?. Also, your supposed to check the timing with the coolant temp sensor unplugged. When I unplug mine with the car running it revvs to like 3k and stays there. If i unplug it then start it, it wont start without giving it alotta throttle then when it does start it revvs to the moon....is this normal?

Im going to check the tps today after i fix the o2 wires also. THANKS so much for the help guys

[spudwiser67]

well the timing should be right around 12* add +- 1 OR 2* deppending on you setup thats kind of a trial and eror kind of thing.

when you check the timing you should have the car running at normal operating temp then unplug the cts the cars idle should change alittle but should not go up to 3k like you said it dose. the racing idle is telling you that you have some thing wrong some where. I would start (I know I know its ben said before) by fixing the o2 wires then clear the codes by diconecting the battery for a min or so then reconect and start the car drive it down the road for a few min then check for any falt codes.

if you find any falt codes find out what the are and fix those probs one at a time starting with the smallest # and work your way up. code 11,12,55, are normal and do not indicate any probs. with all that done you should be able to set the timing with no probs.

[NAJ]

HAPPY BIRTHDAY!!!!!

[mad_psi-shelby]

well didnt get to do the o2 wires today, tried for a minute with a wrench to get out the sensor but it was too tight so I gave up im lazy today.....thanks for the happy b-day!

ill do the wires and get back to u guys. thanks for the help

[mad_psi-shelby]

well fixed the o2 wires and its still doing it. Only when warm tho, cold it idles fine. I think my computer might be taking a shit. Some of the lights flickered yesterday and the tach is skipping and dropping to zero randomly now.....hmmmmmmm

[NAJ]

Does the tach start acting up before the idle problem starts?
I only ask because the last time my tach started acting up it created a power surge in the system, All lights went bright, blower and wiper speed increased, radio went to all static the everything went off for a split second and back on, the tach was no longer working and it blew out both sealed beams and both fog lamp bulbs.
The tach has not worked since and that electrical gremlin has never appeared again.
I did not even to attempt to repair the tach circuit again, just installed an aftermarket tach.
Also, check your engine bay grounds.

[mad_psi-shelby]

hmm engine grounds could have a part in this. I tend to disregard engine grounds i dont know why but i always forget them. Im still wondering, my dad has the same car and his just ran rough all the time, he swapped computers and its ran absolutely amazing since then.....maybe a ecu swap..?

[NAJ]

The braided ground strap from the firewall to the plenum is the main ground for the controller but check them all.
If your Dads car is the same will he let you swap in his controller to see?
Hate to see you spend money on something that may not be needed.

[mad_psi-shelby]

unfortunately his cars an 87 so thats a no go. Would save me some time tho. I dunno im just gona mess with it and test some sensors i guess. If i cant find anything im going to assume its the ecu. Thanks

[puppet]

A bad FPR will do this too. Check it.
I'd give the TB a good cleaning also while you're at it.