New (to me) '99 Maxima - rough idle and other issues

[ncl]

Picked up a '99 maxima GLE with 89k miles about a month ago. I really love this car! It has developed a few issues that I did not notice in the first few weeks of ownership (but temps outside have dropped quite a bit....if that helps with diagnosis).

1) Rough Idle - much more noticeable while in drive. The RPMs bounce and the car "bumps" each time the RPMs bounce. This does not occur all the time at idle, some days/stops it is perfect.

2) Rough acceleration, car stumbles when accelerating, normally when taking off from a stop that the idle was rough.

3) Spark knock (or sure sounds that way). If you really get into the throttle and let the RPMs ride over 4k (or so) the car shudders a bit and sounds like spark knock. If you continue driving "aggressively" : the SES light will begin to flash.

4) At rolling stops/yields the car wants to stay in either 2nd or 3rd gear (can't tell which). I either have to stop completely or really get into the throttle for it to downshift (it works if I downshift manually). If i give it heave throttle to force it to shift, the shift is not very smooth. The transmission fluid has been changed in the last 2k miles with nissan fluid.

I'm assuming that issues 1, 2 and 3 are related.....possibly issue 4 too.

My thoughts/guesses (please give me you input, I would prefer not to blindly replace parts).

Possible solutions:A) TPS - I think this would make sense with all 4 symptoms.B) Spark Plugs/Coils - doubt this would be involved with issue 4C) MAF - doubt this would be involved with issue 4D) IAC - doubt this would be involved with issue 4E)

Thanks for any help , I've searched and searched on this issue, but couldn't find any posts with my same symptoms (a lot of similar issues....but not many with resolutions posted after the fact).

[SR Superstar]

Do you have an aftermarket intake or a reusable air filter?

The oil from K&N and similar filters fouls up the MAF from time to time and causes rough, jumpy idle and even stalling.

I would say head to an autoparts store, get a can of MAF cleaner and try that. It's $6 and has solved similar problems on my car before. In my opinion the stuff is worth it's weight in gold.

If it doesn't solve your problem you're only out $6 and your MAF will be clean.

Just a thought. Sorry I couldn't be of more help to you.

[loystock]

I do agree with SR. It's a practical and cheap solution. A dirty MAF sensor can give you all sort of problems without turning on the CEL. Autozone and other parts store have CRC MAF Sensor cleaner. Use that to clean the MAF sensing element. DO NOT TOUCH THE SENSING ELEMENT. You also have to clean the MAF sensor connector and then apply dielectric grease to prevent corrosion.

You may also have a 'sticky' throttle cable which shows up particularly during cold weather. Apply WD-40 on the throttle cable and its connection to the throttle body.

Autozone offers free scan. Engine knock is bad for engine components. If you have good gas and you have knocking, it's possible that you have a bad/failing Knock Sensor. However, a bad KS will only store a fault code (DTC P0325) but will not turn on the CEL. So a scan may show 'ghost' code(s).

[SR Superstar]

^^ Nicely said. +1

[ncl]

OK, I cleaned the MAF last night (twice) and still have the same symptoms. I also cleaned/lubed the throttle cable.

Could the MAF actually be bad? Would it throw a code if bad?

What about the knock sensor? Would/could it cause a rough idle/acceleration as described? Part of me thinks it is working, due to the fact that when the engine knocks the SES light flashes....

Thanks for the suggestions!

Nick


Modified by ncl at 11:02 AM 12/31/2009

[loystock]

Yes, a bad MAF sensor should trigger the CEL.

Did you get a scan? You may have DTC Code P0325 (Knock Sensor). The ECM and the KS work together to prevent knocking (pre-ignition) by retarding the ignition. If the KS is bad, the system will not know that there is pre-ignition but the ECM should set a fault code (but no CEL). The KS resistance is normally @ 550K ohm. It's also possible that the KS plastic housing is cracked.

Also, if you have not replaced the spark plugs, then they are due. The OEM plugs are rated up to 105K miles but most owners replace them at 60K or 90K miles. Hopefully, the coils are OK. I suggest that you buy OEM or better plugs. We have some issues with Bosch plugs, especially in the Q45.

Also, check the air intake and exhaust manifolds. Make sure you don't have any vacuum leak. With the engine running, spray Carb Cleaner (DO NOT use Brake Cleaner) on vacuum fittings and listen for engine response. Check air filter and replace if necessary. Clean the throttle valve. Use Carb Cleaner but do not spray directly into the TB as it could seep into the sensor assembly. Just spray it into a rag and then use it to clean the body and plate. Be gentle when moving the throttle plate.

An exhaust leak can cause the O2 sensor (s) signals to ECM go haywire.

Yes, the TPS could be a problem too but that should set a fault code.

Better have a scan so we are not shooting in the dark.

Attached is the link to the Maxima FSM. Refer to EC (Engine Control System chapter) to give you a better idea about what we're trying to fix as well as components R&R procedures.

http://www.nicoclub.com/FSM/maxima/1999/

HAPPY NEW YEAR TO YOU AND YOUR FAMILY!!!