Got 2000Max back from mechanic, now have stuttering and low engine power

[jeremyh]

Hello everyone,

First time poster to this forum looking for help.

I took my 2000 Maxima SE with 90,000 miles on it (original owner) into a local mechanic for several issues:

Clutch fluid leak (about a reservoir's worth per week)Replace drive beltsFlush coolantReplace rear brakes

The fluid leak was traced to the rubber hose that's found under the air intake. They replaced this hose. To replace the hose, they removed the air filter housing assembly. They also put in a new air filter.

I noticed my stereo had both the CD and tape ejected, and my radio presets were lost (power disconnected).

When I drove away, I noticed:

Car starts and idles smoothly, ~800 RPM.At light throttle, behaves normally. Sounds normal. Pulls normal.At mid to full throttle, does not have normal pull. RPMs match acceleration rate, which is slow. Feels like "half power". Car stutters occasionally while under mid to full throttle. Doesn't exhibit the same kind of engine howl as it spins up. Doesn't "kick" around 3000 RPMs or so, just keeps climbing at a boring snail pace. May actually be worse than light throttle in terms of power.

Took it back to the shop, demonstrated to the mechanic with a short drive. Mechanic then took it for a drive. His diagnosis is that the clutch is slipping. I called BS. We discussed extensively. Again, RPMs don't spin up faster than the vehicle acceleration. I know what a slipping clutch feels like.

He pointed out that if it was a breathing problem ("Did you leave a shop rag in the intake?"), the engine would hit a wall or sputter at the higher RPMs. The engine will climb to red-line under load, just slowly.

We both agreed that if it was a sensor issue, a connector not getting reconnected, etc, we should see a check engine light. (or is there something you can tell me to say this is wrong?)

Brakes fully release when I take off the parking brake, so it isn't something bad from the rear brake job causing major drag. (Although I did notice I have to pull the hand brake higher than before)

We looked under the hood together, didn't see anything out of place. We focused on the air box housing. Connectors were connected, everything was in place. Pulling the throttle under the hood resulted in an expected RPM increase. We didn't look in the area of the drive belts at all.

Primary symptom remains: Low engine power under full throttle, occasional sputters under half to full throttle, no check engine lights.

Since we were at odds, he said I should take it to the dealer and if they diagnose it as something they did, they will pay for it. I really don't have the time to do this, I waited 2 months with the clutch leak to finally do something about that. I'm hoping it's a simple "look for this hose or connector to be disconnected". Any thoughts on what the problem could be would be greatly appreciated as this one has me very puzzled!


Modified by jeremyh at 1:57 PM 3/3/2010

[maxhopper]

Welcome to NICO.

Wow, that's a very detailed write up you did.

The only thing that pops into my mind as a possible cause are the solenoids that control the switching of the intake runners.

You can read more about this system on page EC-517 http://www.nicoclub.com/FSM/maxima/2000/ec.pdf

See if maybe one of those solenoids are disconnected.

[loystock]

Very interesting problem. We can only make some assumptions based on your description - exhaust is good since it was not 'touched'; no leak in the intake since you did a thorough inspection; brake is not dragging; clutch not slipping; sensors/connectors are good since no CEL.

With low power and very slow but smooth acceleration, it looks likes you have restriction in the air intake. Take out the entire air intake duct, before and after the air filter box up to the throttle body. Check the air filter box and the type of filter used for any sign of restriction/blockage. Do the same for the intake tubes. There is no harm in having a free scan from Autozone as there may be a 'ghost' code but did not turn on the CEL. A Knock Sensor may be defective but the symptoms is usually different from what you have mentioned. You might as well check the Throttle Position Sensor.

[jeremyh]

Thank you for the replies so far!

I spent a bunch of time under the hood and the only thing I saw was that the connecting boot after the MAFS was tweaked (crooked, pushed on too far and potentially gapping), so I thought "aha, it's drawing air after the MAFS". So I removed the air filter housing and while it was out, looked around. I didn't find any unconnected connectors, loose vacuum hoses, etc. Checked the connectors for the solenoids, as that sounded like it had potential because it doesn't run the way it should and can stutter hard around 3000-3500 RPM (bucking bronco) with half-throttle, but they appeared to be in place and still looked dirty as though not touched. Re-assembled the boot connection properly, bolted everything down, took it out for a spin and... no dice.

So the problem still exists. There isn't anything remarkable about the new air filter, if you can point me at how to check the throttle position sensor, I'll check that. Is there a chance the MAF is going defective and the handling during this work aggravated it? Could that present this kind of behavior? I read somewhere else about spraying a cleaner on the MAF so if there's a chance that could help, I'll give that a go. At least now I know how to take the air filter housing out quickly next time.

[loystock]

The MAF, when dirty or has internal failure (cold solder or cracked board) can give all sorts of problem. It could have been mishandled during servicing of the leaking clutch tube. The MAF sensing element is very sensitive and should not be touched with bare hands. There is a screen that protects it from debris, filter side but the other side is exposed. You can try cleaning it with zero-residue contact cleaner or CRC MAF Cleaner (@ $6 from Autozone). Another way to check it is with the engine running, tap the MAF sensor housing, close to the connector and listen for engine response.

Voltage testing may not readily give you problem about the MAF sensor (procedure in FSM, under DTC P0100). An oscilloscope may help, if you have access to it..

Just check the connectors to the Throttle Position Sensors. Procedure on how to test the sensor and switch is given in the FSM provided by 'maxhopper97.'

[jeremyh]

So I threw on a workshirt and some latex gloves before work this morning, pulled it all apart again, and grabbed a can of electric motor cleaner (which is a no residue spray for electric parts, seemed like the perfect choice). Blasted the MAFS a few times, cleaned the screen, cleaned the connector to the MAFS and the connector to whatever the little vacuum housing is that sits next to the strut tower behind the airbox is. Also disconnected the "boost sensor" at the front of the intake and cleaned the connector, and sprayed some on the (o2? air temp?) sensor inside the passage prior to the airbox housing.

Re-assembled and.. it's a miracle! I think that did it. I'm a little guarded still as I have a very short commute, but it sure seemed to do the trick. So I'm guessing the work that was done aggravated a degraded situation (adding a bad connection on the reconnect to a dirty MAFS wire?). I dunno, it didn't look that dirty to me when I started, in fact the whole inside of the tube looked very clean, but you guys did say it's really sensitive.

So thank you again for your help, guys!