[flamed 98 gt]

on my 90 5oh after the car gets hot it starts this rolling idle deal. Sometimes it will correct itself and sometimes it will die. The only codes that I am getting is the egr valve (not running one), smog pump crap (not running it) and the park/neutral safty switch.

[sixpack]

what you mean by rolling idle

[Sleeper_Stang_89]

Like as in u push in the clutch and it dies???

[flamed 98 gt]

Well it surges. I have just heard some people calling it that.

[Sleeper_Stang_89]

have you cleaned your throttle body? check your tps maybe...

[flamed 98 gt]

Both are brand new. It even did this before they were installed.

[flamed 98 gt]

Still doing it any thoughts??

[gotn20]

do the master idle reset that's a sticky at the top of the 5.0 main page. It really works well. I had the same problem but mine was so bad that my car would never idle it would alway's surge and die and now it idle's great. it'll still roll up and down a little every once in a while but it's alot better and it doesn't die

[420HP89GT]

I have the same problem with my GT. Were you able to figure it out?

[86_Notch]

aint fuel injection great ?

[REIGNYC]

Also Check Your Ihac Idile Air Control Module It Might Not Be Working Correctly After All It Is A Small Moving Electric Motor On Your Throttle Body

[420HP89GT]

The IAC valve is new. I just finished building the engine. It has about 100 miles on it. The MAF and injectors are also new. It has a new throttle body that came with a new TPS. The engine starts up and runs great until it reaches max operating temperature. Then it starts revving and cuts off. It only happens once the engine is at max operating temp. If I take it out for a ride it runs fine. Once I get back to my house and I let it idle thats when it starts. The engine temp is about half way up the gauge when it happens. Could the EGR valve be causing this problem? The fuel pressure is steady at 40 psig.

Thanks for your input.

[Modified88Dreamer]

Article No. 90-12-7

^ IDLE - ROLLING - 5.0L HO - THERMACTOR AIR DIVERTER VACUUM SOLENOID VALVE INOPERATIVE

^ THERMACTOR SYSTEM - 5.0L HO - THERMACTOR AIR DIVERTER VACUUM SOLENOID VALVE - DIAGNOSIS AND REPLACEMENT PROCEDURE

FORD: 1987-90 MUSTANG


This TSB is being republished in its entirety to include a separate TAD/TAB solenoid valves and bracket assembly for 1987 Mustangs.

ISSUE: A rolling idle may be caused by a leaking thermactor air diverter (TAD) vacuum solenoid valve.

ACTION: If service is required, use the following diagnosis and service procedure. Refer to the appropriate model year Engine/Emissions Diagnosis Manual, Section 10 for service details for the thermactor system.


An EEC-IV Quick Test may indicate codes 41 and 91, or 44 and 94, or no codes at all. When this occurs, proceed as follows:

1. Run the engine until its temperature is fully stabilized.

2. Turn the engine off.

3. Restart the engine.

4. After waiting for the idle roll to occur, disconnect the vacuum hose at the thermactor diverter valve. Allow it to remain connected to the TAD solenoid.

5. Plug the vacuum hose.


6. After an additional one (1) minute of engine running time, the rolling idle should stop.

7. If this stops the rolling idle, install a new TAD vacuum solenoid valve on 1988-1990 Mustangs or a new TAD/TAB vacuum solenoid valves and bracket assembly on 1987 Mustangs. These parts are located in the RH rear of the engine compartment, behind the shock tower