ryan_89_mustang

My stangs a 87 GT and I have been having some great difficulty getting it to idle when warm. Heres a scenario I go out for a 15 minute drive and stop into the store and I go back out and start the car and it fires right up with no extra cranking but the idle surges up, then down low and the engine cuts off. So I turn it on a second time and hold the revs to around 1500 for say 4-5 seconds then theres a couple small surges and it will idle normal.
Now after all this occurs the next stop sign I go to the car starts to surge which it doesn't do when it's cold but it steadys out after a couple surges. There is also a intermittent stumble between 1500 and 2500 it does not happen all the time or in all gears but this is very annoying and seems like its robbing a lot of power.
And to top it all off I'm getting absolutely horrible gas mileage between 8 and 9mpg!! If anything here stands out to anyone feel free to post your opinions and answers they would be greatly appreciated I'm slowly going broke.

ryan_89_mustang

Bump for the day crowd

brentloftis

MAF conversion or still SD?

ryan_89_mustang

I'm still running SD there are no mods to my car except h pipe and muffs.

brentloftis

From a previous post you mentioned not being able to find a vacuum leak but I would suggest pulling the upper plenum off and replacing the vac line to the map sensor and cleaning the PCV and either plug or replace the line to the charcoal canister.

ryan_89_mustang

I think I found my miss!! I was driving around tonight and I stopped in a parking lot in the dark and popped the hood and saw some arcing on the passenger side near the back of the motor, could this be my problem??

ryan_89_mustang

Bump for a new day.

The arcing was a constant spark I could see in the darkI believe it is happening on cylinder 3 or 4 maybe both. Does anyone know if this would cause my missing problem in lower Rpms?? Thanks,

brentloftis

Yes, are the wires burned or cracked?

ryan_89_mustang

The wires were still nice and soft but the one arcing was an odd wire it didn't match the others and it had a straight boot instead of an angled one. It was taped with electrical tape so I took all that off and the wire was moving back and forth in the boot so I pushed it in and put a bit of electrical tape on it. The problem seems to be fixed now, I am going for another drive in a but I will know for sure when I pop the hood in the dark. Thanks for the help!

Derf00

Replace the wires. Arcing means the spark is not getting to the spark plug, thus your miss. I'm surprised the miss is not more pronounced under load meaning when you step on it and you're at low RPM. There's no power to the car, it just slugs along.