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Why does engine rev up and down when I step on brake?

Why does engine rev up and down when I step on brake?

My engine isn't missing at idle or acceleration. When I step on the brake it revs up and down as if it is going to stop, but it doesn't. I let off the brake it revs/runs fine...

Asked by: Guest | Views: 105
Total answers/comments: 6
bert [Entry]

"There are several different causes depending on the year and engine. If you provide that, I can steer you toward a possible solution. Let me know the year, engine model, and whether it is carbureted or fuel injected.

Some causes:

-vacuum leak

-egr valve damaging fuel line (Toyota recall)

-fast idle valve coolant tube clogged

-fast idle adjustment

-throttle position sensor malfunction

bert [Entry]

"I own a 1988 4X4, with 6 cylinder 3VZE engine and a Manual (Standard) transmission without Cruse Control. The answer lies on p.28 of the Toyota Electrical Wiring Diagram Manual. I was able to clip and tape (1) wire to cure the problem.

My truck would rev up like I was maxing the gas at every stop light. As soon as I got off the brake, everything would go back to normal. I was looking at replacing my $1000 TCCS module but it cured the problem.

If you have an Automatic transmission with Cruse Control it won't work."
bert [Entry]

"I was able to fix this problem when it happened to my 1988 Toyota Custom Cab - 3VZ-E V-6 engine - standard transmission - no cruise control. If you have access to the 1988 Toyota Electrical Wiring Diagram manual, you can find the circuit that's giving you the problem on page 28 (TCCS section 6-1). You start at a 15 amp fuse (15A STOP) that feeds the STOP brake light switch (brake switch). You go through the switch, to connector N5 terminals 4 & 5 (you can check your brake switch function here - 8-14 volts when the brake is applied). You go through N5 and end up at the TCCS ECU module (Toyota Control Computer System - Engine Control Unit) terminal STP-6 under the dash on the passenger side.

This STOP brake light switch wire is not the one that activates your brake lights - it feeds a signal to the TCCS that tells the (AUTOMATIC) transmission to reset to idle and prep to go into 1st gear. I have a MANUAL transmission - and every stop light I came to, sitting there with my brakes on, would rev the engine up so high that everyone was wondering what the idiot in the Toyota Truck was doing. I talked to a Toyota Engineer and told him I was going to clip & tape the wire going to terminal STP-6. After looking through the prints with me, he said - since it was a MANUAL transmission - it looked like it would work. I clipped & taped it - the problem went away and I still drive my 1988 Toyota Custom Cab happily every day."
bert [Entry]

My is a 1934 Ford with 25 years of new life and less than 55,000 miles. It has all Ford running gear, C4, 8.8 rear. 302 ci engine, aluminum heads, headers, air gap intake, 600cfm Demon, and MSD. This problem just started today, and I did find one vac leak but no cure. The car does have good a/c and I have drove it a lot this week. I realize this is out of the norm, but thanks a lot for any help….
bert [Entry]

Hi my Ford mk2 Escort Rs 2000 I have twin 45 Webber’s when I put foot on brake pedal slow down the engine revs up can you help please many thanks Norman
bert [Entry]

Not always a vacuum leak most times is a dirty or broken mass air flow sensor / The pcv valve