95greense

okay here we go. 95 auto max 70K miles. the car idles at ~600 rpms. the car doesn't just have a slight vibration but it actually bucks. standing outside the car you can actually see the car moving slightly. the idle almost sounds as if a cylinder isn't firing. it has a really heavy put-put-put sound. once the rpms pass 1K the problem dissapears and the car drives great. turning the wheel or turning on the AC bumps the rpms a little. no smoke coming out of the exhaust. nothing else seems strange. just at idle. the car just had it's 60K service done. the only thing not done was the fuel filter.

i thought it was an idle problem at first. i cleaned the throttle body and idle control valve completely. it seemed to help but i'm still having the problem. are these symptoms indicative of another problem or do i just need to completely change the idle control valve.

thanks in advance for the help and sorry bout the posts on the other thread.

got rice?

iTrader: (2)

Sound like you're misfiring, hence the 'put put put' sound and non-stable idle.

First, check your spark plugs and make sure they are not fouled. Fouled plugs won't fully ignite the air/fuel mixture. Also run the ECU diagnostic; something like the coolant temp sensor can make your car run rich, causing the same symptoms.

95greense

i'm gonna check the plugs tomorrow but i'll be pretty bummed since i just put in nissan platinum plugs 1K miles ago. just in case though, mis firing plugs will be white right? or was it black? it's been awhile since i've seen that chart showing the plug colors with causes.
regarding the ecu, the only code showing was rear 02 sensor and that's been on for awhile. that couldn't be it could it? i'm pretty sick of taking things off my car and cleaning them. although i gotta say that my intake manifold resembles an oil pan with all the oil and gunk on the inside. i gotta take some time out and clean it.
thanks for the help got rice. appreciate it.

Daniel B. Martin

You said "almost sounds as if a cylinder isn't firing." That's a good clue. Let's go forward on that premise.

If one cylinder is misfiring the problem is spark or fuel. A misfire due to a spark problem usually results in a Service Engine Soon light and one of these Diagnostic Trouble Codes:
0608 - Cylinder 1 misfire
0607 - Cylinder 2 misfire
0606 - Cylinder 3 misfire
0605 - Cylinder 4 misfire
0604 - Cylinder 5 misfire
0603 - Cylinder 6 misfire

You don't have any of these codes, and the engine smooths out at engine speeds greater than 1000 rpm, so let's assume the problem is with fuel delivery.

I believe one of your fuel injectors is not performing properly. There are two tests the home mechanic can make, the sound test and the resistance test.

Sound test...
This test is performed with the engine idling. Use a mechanic's
stethoscope or a length of rubber vacuum hose, and listen to each injector.
All injectors should sound alike. If you find one which makes a different
sound (or no sound at all) you have found a problem.

Resistance test...
This test is performed with the engine off. Use an ohmmeter to measure the
resistance of each injector. This does not require removing the injectors.
I don't know the correct resistance value for the injectors on your model,
but they are typically a low number such as 16 ohms. The important thing
is they should all be equal. If you find one injector with substantially
higher resistance than the others, it is bad. If you find one with zero
ohms (short circuit) that is truly unfortunate, because the injector is bad
and it may also have damaged the Engine Control Module (the computer)
because of excessive current drain.

Measuring the resistance of the front bank of cylinders is easy because the
injectors are in plain view. Disconnect the injector electrical connector
for cylinder #2, measure the resistance, reconnect the connector. Repeat
for the cylinders #4 and #6.

Measuring the resistance of the rear bank of cylinders is almost as easy,
but it is difficult to reach the injectors. The resistance may be measured
at a conveniently located electrical connector. Notice the largest,
thickest electrical harness at the top of the engine. This is the Engine
Control Harness and it is shaped like a U, with the open top of the U at the
driver's side of the car. The U has two corners. Look at the corner
nearest the passenger seat. Just inside that corner you will find an 8-pin
electrical connector. This is connector F131. Disconnect this
connector. Now look at the male part, the connector half with the pins
exposed. They are arranged in two rows of four pins.
The pins are numbered 1 - 4 (top row) and 5 - 8 (bottom row).
Measure the resistance of:
- injector #1 between pins 1 and 2.
- injector #3 between pins 1 and 6.
- injector #5 between pins 1 and 5.
Be sure to measure the PINS, not the female receptacles.

The dealer's shop is equipped with high-tech diagnostic instruments. These are wonderful devices but they are expensive and the dealer has to recover his cost by charging you for diagnostic time. Sometimes the home mechanic can do legitimate diagnostic work with nothing more than a ohmmeter and a rubber tube.