1990 Ford Mustang eractic engine idle and speed

CLYDJOIN

MEMBER
1990 FORD MUSTANG

Engine Performance problem
1990 Ford Mustang V8 Two Wheel Drive Manual n/a miles

i have a 1990 mustang lx 5.0 with a cobra engine I have problems with it leaning out under acceleration everthing has been replaced every sensor, fuel pump relays, ignition ive been through the wiring harness the car was orinallly a 4 cyl car I bought the car after someone had replaced the engine with the cobra engine the car has no emmisions at all on it but the engine ran fine for years the I had a miss at highway speeds then I replaced the ignition pickup in the distriibtor and the fixed that problem new mass air meter calibrated for 24lb injectors, I dont know what else to try I do know when I drive it when its cold it runs fine when it heats up it starts running and idleing bad the after a few minutes when it cools downs while idling it levels out and runs smooth. If u have any suggestions I would appretaite it. When I say I replaced ever sensor thats what I did. Ive been over and over everything on it. Hope u can help.

clyde

4 Replies

JNOVACK

MECHANIC
723 POSTS

It may not have proper power control module and may not be programed to specs for you engine and application remember it had a 4 cylender in it

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Friday, November 7th, 2008 AT 2:51 PM

RASMATAZ

MECHANIC
75,992 POSTS

1990 Ford Mustang eractic engine idle and speed

All parameter sensors replaced-inspect and test the EGR and PCV valves, look for vacuum leaks, check the idle air control valve/motor and do a fuel pressure test.

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Friday, November 7th, 2008 AT 2:52 PM

CLYDJOIN

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I fogot to mention that I changed the computer in it when I bought the car it had a A9P computer which is for a automatic 5.0 I put in a A9L which is for the 5 speed ive changed the fuel pump I have a fuel pressure guauge outside of the car on the cowl it is set between 35 40 psi. The car actuall doesnt acted up until I drive it and it warms up and idles like it s miss firing but as u let it idle and cool down some it smooths out. Like I mentioned ive changed everything on the engine including the tps sensor ildle air control motor, temp sensor, air temp sensor egr valve position sensor, bap sensor, o2 sensors but I noticed when its running rough after a trip down the road I can unplug the o2 sensors the idle smooths out somewhat until cools downs then it dont make a difference in idle quality as u see I covered alot thats why I got on here to see if there is something im missing this is the first fuelie mustang ive fooled with for as modifying one.I like the carb versions better lol. But I the mods ive made r just on the outside of the engine I have 24lb injectors c&l 76 mm mass air meter calibrated for the 24lbrs, bbk70 mm throttle body along with cold air intake gt 40 upper and lower intakethe ignition is all new except for the distributor housing. Coil i, gnition module, MSD wires plugs, magnetic pickup. Long tube headers. Ther was no emission equipment ion the car when I got it it had a off road h-pipe and no cats r smog pump but the car ran fine for years like that all the codes come up with e emission codes but it hasnt made a difference in performnce, the problem start when ihad a bad miss at highways speeds I traced it down to the magnetic pickup in the distibutor then after that this other prob came up. It really acts up between ilde and 2000 rpm then it smooths out alittle, it cuts out at wide open throttle alittle surges in and out too. Hope u had some answers for me. Im out of them lol.

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Friday, November 7th, 2008 AT 3:51 PM

RASMATAZ

MECHANIC
75,992 POSTS

Try below and see what happens and also test the TPS voltage

Here's how to clean the IAC valve:

Disconnect the air intake ductwork from the throttle body.

Start the engine, then increase and hold the idle speed to 1,000 to 1,500 rpm.

Spray the throttle cleaner or engine cleaner into the throat of the throttle body, aiming for the idle air bypass port (usually located on the side or top of the throttle body opening). Give this area a good dose of cleaner (about 10 second's worth).

Turn the engine off to allow the cleaner to soak into the IAC passageway.

Wait about three minutes.

Restart the engine, rev and hold at 1,000 to 1,500 rpm, and repeat the cleaning process again.

Turn the engine off again, and reattach the air intake ductwork to the throttle body.

Start the engine and rev and hold to 1,500 to 2,000 rpm until no white smoke is coming out of the exhaust pipe.

If this fails to make any difference, you can remove the IAC valve from the throttle body and spray cleaner directly on the tip of the valve and/or into the ports in the throttle body. Let the cleaner soak awhile, repeat as needed, then reinstall the IAC valve, start the engine and run it at 1,500 to 2,000 rpm as before until no white smoke is seen in the exahust.

If the idle speed still surges after this, the IAC valve is defective and needs to be replaced.