Hesitation at low throttle only.

[StageLeft]

04 MPV with 70k and auto tranny and 6 new oem plugs.

Idle is perfect. Full throttle is perfect. Moderate throttle is perfect. Mild throttle the car hesitates as if it's not getting enough fuel or not firing properly or something like that. It's not massive but it's definitely there and I'm definitely not dreaming.

Last year I had a CEL from a bad rear coil. I replaced that single coil. I have no CEL now (not even a hidden one; I did check at the auto store). This symptom is not quite exactly as it was before, but I am still leaning toward replacing two more coils. For some reason I assume if this is coil related, it's the two rear very-hard-to-get-at ones, so I am leaning to replacing those at around $55/piece and see what happens.

I doubt this is idle air valve, as idle is perfect. It could be the PCV valve, but a common problem with this car is the pcv tube deteriorates and I've already replaced that. I don't think it's fuel related as full throttle is perfect. FWIW I put through a bottle of Chevron Techron every 15k or thereabouts.

--

I will, if anybody can solve this beyond affirming the idea to replace those two coils, put you at the top of my sig for a month and I will revel in your greatness.

*UPDATE 2/20/2009*

I cleaned the MAF thoroughly and the hesitation is completely gone for me. I cannot reproduce it. MrsSkoorb says she can at times but that it's much better. Presumably the MAF cannot be cleaned further and will die at some point, but now I actually don't hate driving the van again, whoot. A cheap fix.

Thanks much to those who recommended MAF Before I finally did it:

bruceb
Marlin1975

 

[maluckey]

My N0. 1 pick is one or more O2 sensors are either bad or clogged. Cracked or bad plugs and/or wires can do similar things. Is your mileage dropping? If so, O2 sensor is no. 1 culprit.

 

[dug777]

Spark plugs, leads or coils.

 

[Dman877]

I had a buddy in high school with like a 96 MPV. He would hit the gas and about 2 seconds later the car would start moving. Turned out to be mice in the tranny

 

[dug777]

Originally posted by: Dman877
I had a buddy in high school with like a 96 MPV. He would hit the gas and about 2 seconds later the car would start moving. Turned out to be mice in the tranny

Like mice paste? Or live mice, pinky & the brain style catastrophising things down there?

 

[dug777]

Why do modern vehicles have many smaller coils? My 323 just has one beefcake coil for all four of its mighty, thrusting cylinders

EDIT: I assume that means modern vehicles don't have distributors?

 

[bruceb]

Yes, it is because 99% of most cars are distributorless now. Like the GM V8 with 1 coil for each cylinder and plug wire of about 6" or so in length.
It does work nice that way and is easy to service.

As to the OP's problem, I would suggest the following be checked:

Fuel Pressure at Idle .. possible clogged Fuel Filter or bad Fuel Pump / Pressure Regulator
Check and clean the Mass Air Flow sensor (carefully so as not to damage it)
Do a professional High Pressure cleaning of the Fuel Injectors
Check the Air Filter is not clogged
If access to a real time data logging scan tool, see what the O2 sensors are telling the computer.
I would suspect the O2 sensor Before the converter might be defective.

 

[dug777]

Originally posted by: bruceb
Yes, it is because 99% of most cars are distributorless now. Like the GM V8 with 1 coil for each cylinder and plug wire of about 6" or so in length.
It does work nice that way and is easy to service.

As to the OP's problem, I would suggest the following be checked:

Fuel Pressure at Idle .. possible clogged Fuel Filter or bad Fuel Pump / Pressure Regulator
Check and clean the Mass Air Flow sensor (carefully so as not to damage it)
Do a professional High Pressure cleaning of the Fuel Injectors
Check the Air Filter is not clogged
If access to a real time data logging scan tool, see what the O2 sensors are telling the computer.
I would suspect the O2 sensor Before the converter might be defective.

This may be a stupid question, but why is it easier to service? The single big coil packs don't ever seem to go, but i get the impression these dinky coils go relatively regularly?

 

[HannibalX]

My diagnosis: The torque converter is toast, what you are feeling isn't engine hesitation it's the torque converter "shimmy'ing" because it's burnt to a crisp.

 

[Vette73]

With 70k the mass air flow sensor may be dirty.

My Corvette would spark knock like crazy until i cleaned it. My Mazda B4000 would have a really bad hesitation under light throttle.

But you have to be very carful when cleaning.

 

[StageLeft]

Originally posted by: maluckey
My N0. 1 pick is one or more O2 sensors are either bad or clogged. Cracked or bad plugs and/or wires can do similar things. Is your mileage dropping? If so, O2 sensor is no. 1 culprit.

I think mileage is ok. I will say that the car did pass inspection (and I think it includes emissions) this past December, but it often smells like it took a fart after we're done driving, especially when it's in the garage.

Cleaning the MAF is free, so I think I will try that. I have carb cleaner and brake cleaner, both of which I presume I should not clean it with. I'll google how to clean it, thanks for the idea...

 

[Vette73]

^


Q-Tip and some rubbing alchol. Be very careful when doing it. Don't push on the element just kinda let it slide by it.

 

[StageLeft]

Originally posted by: Marlin1975
^


Q-Tip and some rubbing alchol. Be very careful when doing it. Don't push on the element just kinda let it slide by it.

What about electric parts or MAF cleaner (that exists in cans but probably harder to find)?

 

[bruceb]

Re the query about why multiple coils are easier to service, is that you can pinpoint (thru the car OBDII or CAN computer) exactly which cylinder has the problem. If a coil is bad, it can be replaced in about 5 minutes and you do not have to worry about how to route ignition wires. I never said it was cheaper, but it is more reliable.

 

[StageLeft]

Originally posted by: bruceb
Re the query about why multiple coils are easier to service, is that you can pinpoint (thru the car OBDII or CAN computer) exactly which cylinder has the problem. If a coil is bad, it can be replaced in about 5 minutes and you do not have to worry about how to route ignition wires. I never said it was cheaper, but it is more reliable.

Unless you have a bad coil or coils and no CEL fires. I had this problem on my maxima and other than playing replace-one-at-a-time I just did all six to the tune of $60/piece and it fixed it. It was a bit notorious in that car to have coil problems and no CEL fire so generally people would replace all of them!

 

[Vette73]

Originally posted by: Skoorb

Originally posted by: Marlin1975
^


Q-Tip and some rubbing alchol. Be very careful when doing it. Don't push on the element just kinda let it slide by it.

What about electric parts or MAF cleaner (that exists in cans but probably harder to find)?

The MAF cleaner just sprays as far as I know. Electric parts cleaner if not in spray form may work also. But with spray it works by getting it so wet that the dirt falls off. So for my mazda that would not have worked the way the MAF is housed. The Corvette MAF it may have. But I have Qtips and rubbing Alc. in my house.

 

[Howard]

Dirty throttle body?

 

[91TTZ]

Your throttle position sensor could be bad.

 

[BUTCH1]

Originally posted by: 91TTZ
Your throttle position sensor could be bad.

Good guess, I'm gonna go with EGR valve, they start operation in the RPM range OP is seeing the problem at and the do get dirty over time..

 

[RU482]

I had a similar issue with my Impala. Replaced the fuel filter and it went away.

Cheap and easy enough to do, might as well try it

 

[Colt45]

vacuum leak!

 

[Hyperlite]

timing. stuck PCV valve will also do this. had it replaced twice in 11 years so far in my car.

 

[StageLeft]

Updated

 

[Vette73]

Originally posted by: Skoorb
Updated

:thumbsup:

Also spray out the throttle body if you have not done so. May help a little more. Not as much as a clean MAF but every little bit helps.

And WTF is up with your Mazda? Seems like once a month you have a new problem with it. My 160k Mazda, Saab 900se with over 100k and a bad history, etc... did not seem to have as many problems as yours. Or Ms Skoorb is messing with it to keep you out of the house?

 

[StageLeft]

Originally posted by: Marlin1975

Originally posted by: Skoorb
Updated

:thumbsup:

Also spray out the throttle body if you have not done so. May help a little more. Not as much as a clean MAF but every little bit helps.

And WTF is up with your Mazda? Seems like once a month you have a new problem with it. My 160k Mazda, Saab 900se with over 100k and a bad history, etc... did not seem to have as many problems as yours. Or Ms Skoorb is messing with it to keep you out of the house?

I did the throttle body with carb cleaner a little while ago when doing the ignition coil.

Believe it or not, I have another thread about my mazda coming up, but I didn't want to swamp the forums I actually like the van, this is just growing pains or puberty, perhaps.