2001 MPV Rough Acceleration in High Humidity

I have noticed that my 2001 MPV, on foggy, high humidity, mornings will initially accelerate roughly, as if the engine is missing, until the engine warms up. Under low load operation, when the engine is cool, it isn't as noticeable. However, if you are trying to accelerate into traffic, there is a definite loss of power evident.

History - I bought this vehicle used about a year ago and this problem has existed from day one. Recently my air intake manifold gasket was replaced because it was leaking badly and the vehicle was barely idling. Prior to this I had a P300 code that the dealer said was related to the coil pack. I replaced this, the plugs and ignition wires. Even after this work was done, the same P300 code would set and the vehicle would idle badly and run essentially on only 4 cylinders. The dealer checked the vehicle over thoroughly but really could never explain why the code continued to set. Howerver they did check all electrical plug connections. This problem has not returned for several weeks now.

I don't know if any of this stuff is related. I would appreciate any thoughts re the cold engine/high humidity rough running condition. Thanks

change your spark plugs and plug wires.

cold misfires on these vans are usually caused by high carbon buildup on the exhaust valves. a "de-carbon" service may help. if after a de-carbon service is performed i'd reccomend having a compression test done as i've seen burnt exhaust valves as well.

I'm not familiar with a de-carbon service. What does this entail and is it expensive?

I found a huge amount of carbon build-up in the aluminum intake manifold on my daughter's '00 (120k miles). If you just drop the throttle body you can inspect the area where I found all the carbon. (I think this was all caused by a dirty intake air filter ... but not sure).

If you find the manifold loaded up ... it's not too hard to remove it for a cleaning.

decarbon services usually consist of 3 things...

1. a gas tank additive

2. a thorough throttle body cleaning

3. and most importantly, a cleaning chemical that is sucked in through a port on the intake manifold. the chemical should be allowed to soak for as long as possible... the chemical sits in the intake and on the valves and in the combustion chamber and breaks up the carbon deposits. when the car is started and ran the chemical and broken up carbon are blown out with exhaust gases, usually leaving a large cloud of white smoke. i reccomend you allow a trained professional to do this procedure as if the chemical is sucked in too quickly or without an orifice you run risk of hydrolocking your engine.

I am having exactly the same troubles on my 01 MPV-90000miles. On a cool, dry morning no problems at all. On a humid day it hesitates and almost dies with no check engine light.

Why in the heck does this engine do this so frequently when my previous experience with several other brands had absoluetly never had this??? My dealer says $550 to do the throttle body, "air intake sensor" and de-carbon. We did this at 50,000 miles too!

I think I'd rather deal with a $500 timing belt every 90000 miles than have to do $1000 work on the throttle every 90000 miles. I'm way less than impressed.

Possum5,
Though the task is a bit labour intensive ... lotsa cleaning, ... it's not very difficult skillwise. No reason anyone with some tools and a little skill level should not try it.

After cleaning the intake, make sure the; (1) air filter, (2) pcv valve, and (3) EGR tube are all in good shape.

just listen to mazdatech177 high carbon will only cause spark knock. The humidity is causing the spark plug wires and plugs to short out. Replace your plugs and wires. problem solve unless you have vaccume leaks.

Thank you both for the quick reply. I got into looking at the plugs, jeez they are buried! Any tips to get in there without tearing off the whole top of the engine?