hi all

i have a 1992 mustang gt hatchback and ive been having some issues with it.

First of all, it has an idling issue. Whenever i start the car when the engine is cold, it idles like crap. But everyonce in a while, when i start the car when the engine is warm, it idles perfectly fine.

There is also another issue with the engine. When you are driving the car at around 1500-2000 rpm, it "misses". The car jolts foward almost like its missfiring. Could this be a bad spark plug?

 

1st check for codes do a key on engine off test. could be simple like a vacuum leak or more but rule out any code problems 1st before moving on. The miss could be a bad plug(s), plug wire(s), coil ( when they get bad and hot they will flatten out at higher rpm), cap/rotor. the coil can be tested but it needs to cycled enough to get it hot. could also be dirty fuel filter, weak pump, etc also can be tested. weak fuel pressure at high rpm can cause this problem also. start at the cheaper easy stuff 1st and work up. check plugs, wires, cap/rotor, etc, etc. also could be code related, dirty maf so you have some stuff to start checking and report back.

 

If I recall, 1500-2000 RPM is where the EGR kicks in. I'd definitely pull codes because an EGR fault is likely to throw one. I'd also check vacuum, as mentioned, and the EGR valve body itself.

 

The cold start idling problem could mean a bad IAC. I'd give that a look if the above mentioned suggestions don't help you any.

 

here are the results of the key on engine off test

these codes were gathered while the engine was NOT running
11/11
96
31
96
31

also, the check engine light will come on for a little bit and then turn off while i am driving the car

 

code 11 is pass ? so I don't know why you got this with codes.

Code 31 is an EGR code "EVP circuit below minimum voltage" . could be a vacuum issue, on the pass side strut tower is the vacuum solenoid for the egr. could be a faulty egr sensor this is mounted on the back of the egr. the egr could be sticking from carbon build up. I had this code and mine was both the solenoid and egr valve position sensor.

this is what the egr soleniod looks like mounted on strut tower:



code 96- fuel pump circuit failure or high speed fuel pump relay circuit failure. could have a faulty intertia switch ( could have giving you the or fuel starving feeling) check for 12V going in and coming out ( make sure it is reset if tripped) . could be an intermittent trip that may not come back, but it could be in teh fuel pump, fuel pump relay circuit, etc.

 

I had code 31 on my 89 gt and I had a bad EGR valve and EGR valve position sensor. Like skunk21 says do make sure your vacuum lines are good. I'd strongly recommend a vacuum tester, I find mine invaluable.

 

@skunk21:yea i was confused too when it gave me the pass code and spit out the other codes...any idea on the cost of the egr soleniod..and if its in the fuel pump, im assuming the whole pump has to go

@otmshank: Where would i get this vacuum tester?

 

Do some testing, ie fuel pressure,etc. I would work on code 31 1st and see if that cure your problem. I have seen the code 96 come up and not present a problem and actually clear out. EGR sensor can be around 30-50 depending on brand and store. once you do a repair clear the codes:

Clearing Codes:
1. Disconnect battery (-) terminal for 3-5 minutes.
2. The above will cause a code 15 (Keep Alive Memory (KAM) Test Failed) to be logged since power was removed from the system memory.


then let it go through a run cycle. Make sure you verify vacuum is working, the egr isn't sticking and the egr diaphragm is good before clearing the codes.

 

All the advice above is spot on, how many miles on your engine? Vacuum is very important and all your sensors checked and cleaned. I had the same thing happen to my 87 after doing all the small stuff and tune up it still had a stumble.. took the plenum of and took one injector out and it fell apart... I replaced them all and my 180,000 mile 87 runs like brand new! An injector can be partially clogged and do this...

 

Any auto parts store should have them. If you don't feel like going out there's always summit http://www.summitracing.com/parts/WMR-W80594/.

I ended up hooking the tester and running the hose temporarily into the cabin so I could see what was happening while I was driving.

 

Someone also told me that it could be an oxygen sensor( a bad one of these sensors causes rough idling)...does this have a specific error code?
@jacostang: the engine has about 80,000 miles on it

 

Work on the knowns do not throw parts at the car. 02s will toss a code and you do not have any ( they are in the 40s iirc, like 41, 42, etc. I would have to look them up).


right now you have an EGR code and that also causes your problem.

 

got an update on the car

was driving it yesturday and it had the same problems as before ( rough idle and the engine miss firing or whatever)
but after i stoped the car to go into the store and started it back up, the car ran perfectly fine (idled fine and the engine wasnt miss firing)
keep in mind i havent fixed anything in the car yet

 

My car is doing the exact same thing only mine is throwing 02 codes of 42/92 rich, no switching detected. But just like you said I can turn mine off at the store and get back in it, runs fine. Mine sometimes will start off the day great and run great the whole day then run like crap the next. anyone els have ideas, I have a 347 stroker, afr 185 heads, msd ignition, and has the egr blocked off, and when it is running bad it gets worse as the engine comes up to closed loop operation. a real bad stumble at 70 in 5th gear minimal throttle 2000 rpm. Has driven me crazy for a couple of months, drinking fuel like crazy.