General Question

robmandu's avatar

Weird engine hesitation and stuttering after warmup?

Asked by robmandu (21210 points ) March 24th, 2011

When I first start up my truck, it runs fine and accelerates fine for the first several minutes. It even seems okay for a few minutes after the coolant has reached the normal operating temperature.

But then the engine will begin to slightly stutter, almost imperceptibly at first, and gets steadily worse… jerking a bit while I’ve got pressure on the pedal.

It’s not the transmission. I can reproduce with no load on the engine, the transmission in neutral.

At first I was thinking it might be the fuel filter… but I’d expect that to happen all the time, not just after warming up.

Maybe the spark plug wires? But again, why only after it’s warmed up?

I do run premium fuel all the time to prevent spark knock that occurs, especially on warmer days.

I’ll probably take it into the shop tomorrow for evaluation. What should I expect them to suggest? What should I be wary of?

——
2000 Nissan Xterra XE
3.3L V6
4WD, manual transmission
115k miles

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15 Answers

geeky_mama's avatar

The fact that it’s when you have pressure on the pedal makes me think it might be related to the throttle—either cable or the sensors that tell the throttle how far open it is..
I have a newer Mazda (2007) with only about 50K miles (also manual transmission) and the throttle body failed recently..with similar symptoms to what you describe. (But…this seems to be a problem with my model of car..they haven’t recalled it yet or put out a service bulletin, but I had no trouble finding others with the same problem with my car make/model.)

Anyway – if it’s the throttle body it’s not a very expensive repair (well, in comparison to needing a transmission)..and you might find you get better gas mileage after the repair, too.

Good luck tomorrow – hope it’s an inexpensive fix.

Scooby's avatar

What about the air filter?? Do much offroading??

filmfann's avatar

Fuel filter. When the engine is cold, it is pumping more gas in the mix.

robmandu's avatar

@Scooby, new air filter put in about a week ago.

@filmfann, so… when the engine is cold, more gas is in the mix and the problem isn’t as noticeable… but as the engine warms up, the fuel-to-air ratio drops and then when minor clogs are encountered, it’s a bigger impact as there’s less fuel already and it’s cutting out the fuel flow almost entirely… that right?

Russell_D_SpacePoet's avatar

I have seen worn plug wires start to misfire after the vehicle warms up. You might check them if they ave not been replaced in a while. Partially clogged fuel filter can also cause similar symptoms.

Scooby's avatar

You may have a faulty earth, check your earth straps? :-/

Skaggfacemutt's avatar

My auto mechanic son would know. Too bad he’s always at work. :( He taught me enough to know that it has to be fuel, air or spark. Sounds like a bad spark plug or wire to me. A good shop will do a diagnostic on it and be able to tell.

robmandu's avatar

[Update]: Not the fuel filter. The on-board diagnostics don’t report any trouble codes.

Still investigating.

Skaggfacemutt's avatar

I don’t mean on-board diagnostics, I mean the big, commercial diagnostic machine at the repair shop. Still think it’s a bad spark plug or wire.

robmandu's avatar

[Update]: Not the fuel injectors. And they’ve eliminated the mass flow sensor as well.

They say the catalytic converter is getting so hot, it glows cherry red. They went looking under when they heard the ticking sound of cooling metal after shutting down the engine.

Thing is, it’s made the ticking sound since I first drove it home from the dealer back in ‘99. So I’m kinda worried they’re chasing down a red herring.

Their opinion is that a red hot cat means restricted exhaust flow… which could cause the symptoms here.

I’ll have to check back with them about the spark plug cables.

Scooby's avatar

Has it got a Turbo? :-/

robmandu's avatar

Nope, no turbo. Not available in 2000 models.

[Update]: testing shows that the fuel regulator is pumping up to 55 psi when it should only be at 35 psi.

Gotta wait until Monday for the replacement part to arrive, though. :-/

robmandu's avatar

[Update]: Now they’re saying it’s the ignition coil. And that the ignition coil is part of the distributor cap assembly on the Xterra. That part alone costs $350. Throw in new spark plugs (overdue) as well as spark plug wires.

Hope I can get it back today and let you know how it runs.

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