Cruise control runaway

[DBF]

1992 D-250 Auto.

I'm running down the road, turn cruise control on, and hit Set. The RPM jumps up and the truck increases speed rapidly with black smoke, lots of noise, everybody running for cover and wondering what that nut is doing.

Touching the brake pedal turns off the cruise control and all goes back to normal.

The diagnostic tree in section 8H of the FSM doesn't have a path for this problem.

Obviously, the adjustment clip is installed on the bell-crank end and the clevis clip is installed at the servo, otherwise the servo wouldn't pull the cable and get full throttle.

Vacuum is also good, or it wouldn't work. Plus, I measured it at 27" idling.

The servo plug electrical contacts have been cleaned and the electrical continuity checks on pp. 8H-7, continuing on 8H-8, are what the book says is correct.

There are no unexplained Fault Codes - just 12 & 55. No lights on the warning panel.

For maybe-related things: The speedometer is smooth, so no sensor problem there. The transmission shifts into O/D normally (pot installed vice TPS).

I'm stumped. I guess I'll clean the contacts on the PCM plug/socket next, but I sure could use anyone who's had this problem and solved it to speak up.

Regards, DBF

Oo.

 

[cerberusiam]

Have one that does the same thing, the set button is busted but it will work with one little problem. :-laf



Gotta be a problem with the momentary that ain't no more.

 

[JLEONARD]

:-lafDon't have any toyota parts in ther do ya? LOL

 

[jwinnie]

About all you have left to check is the accel/coast switches on the wheel and the pcm plug contacts.
My problem was a little different. I would set the cruise and after about 5 seconds the truck would slowly (see edit) accelerate to warp speed.
A new pcm solved the problem.

pcm or ecm

edit: my engine is basically stock, so it does everything "slowly"