PovertyPony

Hello, I've got an interesting issue with my 1994 Mustang GT.

It's mostly stock, save a Powerdyne supercharger kit and exhaust. I think it's got a 6# pulley on it.

Anyways, the car surges at idle pretty bad, going up and down, and eventually it will dive down low enough to cut off. It drives fine though. Also, when the AC is turned on, the car usually idles great. It will also stay alive if I just slightly rest my foot on the gas pedal.

If we disconnect the supercharger belt and run the car without the blower running, it also idles perfectly.

Opinions? Blower surge? Any techniques for eliminating it?

Thanks in advance guys!

AdderMk2

FULL list of mods please

Venomantidote95

Is it tuned or have a chip burnt for the blower?

jthorn9

See for an issue like this the IAC and TPS sensors are usually to blame, however I don't think it's the case, although it would still be a good idea to look them over.

I would start looking over the supercharger unit itself and make sure that the impeller is spinning freely with no obstruction. I know powerdyne isn't exactly known for making quality superchargers.

Now if both of those check out it could be a vacuum leak. It sounds like when the S/C is being slightly spooled at idel that the slight boost in vacuum could be blowing through a leak causing a short term loss in vacuum and poor idel. I had a similar problem in my 5.0 a long while back, the upper intake wasn't seated all the way to the lower which caused the idel problem. It was so minute that my boost/vacuume gague didn't pick up up, but a smoke test did.

PovertyPony

Thank you for your insight! I was thinking possibly the same myself, I'll try to have a more rigorous vacuum leak test performed. TPS and IAC will also be checked out.

Also sorry fellas for being slow, cable outages. =[

List 'o mods:
Powerdyne S/C
BBK Headers
Stock midpipe (For now, ****'s coming off ASAP, it was put on all ***** nilly to pass VA inspection and there's an exhaust leak at the driver side flange, I'll address that when I put my H pipe on since I'm in NC and we don't give a crap about emissions)
Flowmaster mufflers
3.73 gears (Dunno why that would matter)
All the typical bling that's non mechanical (Rims/Cowl/Springs/Etc...)

Ummmmm, I think that's it. There's a fender-well intake, dunno if that's stock with the kit or not. It did have a raunchy air filter when I got the car, had that cleaned up.

Also, if it is a vacuum leak/tps/iac, then why does it not idle crazy when the AC pump is on?

Oh, and when my roommate had the S/C off of the car the other day he said it spun well and moved air good. We're not S/C experts or anything, but seems if there was an issue it would have resisted being turned by hand. (Had to pull it to change a crappy Advance alternator)

And TBH I'm not 100% certain that the car has been tuned, good at least. I figured it would run like total *** under full throttle and probably have blown up by now if it hasn't been tuned. No wideband to report on air/fuel behavior, but it runs like a champ other than the idle, no knocks or anything. Where do I look for a chip, the kick panel by the passenger's feet?

Could timing be an issue?

Venomantidote95

Yes plugged into the ecm passenger side! Did it run goood before the S/C was removed to change the alt?

4rdnut

The clue i see is, if the ac is on, it idles perfect because the ac circuit raises the idle for the extra load from the ac compressor being engaged and if you disconnect the super charger belt your relieving the load of the sc compressor and your idle is fine, so why dont you just raise your idle higher at the throttle body so it can handle the sc load, also make sure your cold air intake is smooth with non turbulent air, so it won't throw off your mass air sensor reading and make sure you have no umetered air leaks between mass air meter and throttle body.

g3mustang

^^^ thats what i say. also try clocking the maf may help i had to turn mine to 3 o'clock and idle good

PovertyPony

Thanks for the suggestions, will be trying those!

PovertyPony

OH and it idled like crap before the alternator and stuff came off.