Surging 2002 Mazda Tribute v6

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#1

We’ve owned this 2002 Mazda Tribute v6 for six years. Recently, the car has become somewhat dangerous to drive. While driving down the road at any speed, releasing the throttle does not result in the engine decelerating or returning to idle. Instead, it continues to hold the speed steady for 3-5 seconds before the RPMs drop. At lower speeds (~5mph or so) the car will even accelerate a bit, which can be a problem in tight parking situations. At higher speeds (e.g. on the freeway) releasing the throttle has no effect for a few seconds (ie it does not decelerate), which can be very surprising if you’re responding to suddenly slowing traffic. The brakes can, of course, overpower the engine, but you do have to push harder to get the same braking effect as if you were not fighting against the engine. Releasing the throttle and shifting into neutral while driving causes the engine to rev quite high (3,000rpm) for the same 3-5 seconds before dropping to a steady idle, but it does allow you to brake normally. Shifting back into Drive while in motion but not touching the throttle causes the engine to decelerate the car normally. Touch the gas even briefly, though, and the engine will once again surge.

Oh, and turning the steering wheel from side to side, as you might do while parking, also causes the engine to surge, though not as much as it does when I touch the gas pedal. Also, I’ve disconnected the throttle and cruise control cables and worked the throttle plate by hand. Doing so causes the RPM to rise, as you expect, but it does not immediately return to idle when the throttle plate snaps shut. Instead, the RPMs stay around 12~1500 for 3-5 seconds before it drops to idle.

Over the years, I’ve replaced the throttle position sensor, idle air control valve, and other normal maintenance items. I used a meter to troubleshoot the IAC and TPS and used propane to look for vacuum leaks, but everything is within spec. There are recall notices related to unintended acceleration for these vehicles, but those are reportedly caused by interference between the engine cover and cruise control. I do my own maintenance and don’t like engine covers, so I removed the cover from this car shortly after buying it; the engine cover cannot be causing this problem. I have disconnected the battery for an hour to reset the computer, but that has no effect. There are no trouble codes that show up on a OBD-II scanner, and the CEL is not illuminated. There are many internet reports of this problem, but thus far I’ve found none that indicate a solution.

Thoughts?

Thanks,
Jeff


#2

According to my information, this vehicle has an accelerator cable that is the subject of a recall IN ADDITION TO the one that references the engine cover clearance problem. I’ve posted the info for you. My money is on the accelerator cable being the source of the problem.

VEHICLE SPEED CONTROL:CABLESRecall for 2002 Mazda Tribute
Recall Announced:DECEMBER 10 2004
NHTSA Reference:#04V583000
Number Affected:121,000

Summary: On certain sport utility vehicles, the accelerator cable may prevent the throttle from returning to the idle position.

Consequence: An unexpected increase in engine idle speed may increase stopping distance and may result in a vehicle crash.

Fix: Dealers will replace the accelerator cable. The recall began on January 28, 2005. Owners should contact Mazda at 1-800-222-5500, option #4.

For detailed information & supporting documents, see the official NHTSA page concerning recall #04V583000 »


#3

You should check that the recall has been done either way. But if it does about the same thing with the throttle cable disconnected (as it sounds like it does), and you are sure that the throttle plate does snap closed fully on release then I’d be guessing that the IAC is gummy (just clean it - you don’t necessarily need to replace it) or otherwise has a control issue.

I would also check the intake snorkel for hidden splits. And pull the throttle body, clean it, and give it and the IAC a fresh gasket. One of the things that happens when you snap the throttle shut is that you get a brief vacuum spike. If you had a small little vacuum leak that bit of a spike might make it show itself. I’m not entirely sure that makes sense - but I’m still thinking about it.


#4

Good ideas above. Undiagnosed vacuum leaks can cause this symptom too. I had this problem big-time with my Ford truck on one occasion, and it turned out to be a broken diaphragm in the vacuum device which directed warm air into the engine when the coolant was cold. Unmetered air was getting into the engine through that vacuum actuator. Replacing it fixed the problem straight away.

These kinds of vacuum leaks are difficult to diagnose with traditional methods like you have already used. A brake booster diaphragm leak is another common cause, so that’s a good thing to check. Any method that air can get into the engine remains a suspect. Sometimes you have to use a pair of locking pliers (hemostats work good for this) and clamp down on each vacuum line one by one and note if there is any difference in idle speed.

You mention that turning the steering wheel speeds the idle. This is probably normal, as there is usually a vacuum valve in the power steering pump that allows extra air into the engine when turning the steering wheel. This is to avoid having the engine stall when parking, as the power steering pump puts extra load on the engine. That valve in the power steering pump could be leaking when it shouldn’t.


#5

For the RPMs to stay high with the trottle snapped shut means that air HAS to be getting into the engine somehow. If all sources of a vacuum leak have been examined, then the IAC is the prime suspect. As mentioned, a gummy or slow to move IAC may be your issue.


#6

The very first thing I would do is thoroughly clean the throttle

Perhaps it’s not snapping back to the fully closed position because it’s gummed up


#7

Hi Jeff,
I have the same problem. How were you able to fix your car?
Thanks in advance,
Noty