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MORE: Engine idle questions
Car Idle Question and Answer - This category contains featured questions
as examples. They relate to most vehicles.
Question: 1967 Ford Mustang 289
2 bbl, mileage 49,000. The owner had just taken it out of storage after 5 years
and it won't idle right, but it has gobs of power and smoothes out perfectly above
2000 rpms. He bought a new carb. It still does the same thing. He did COMPLETE tune
up on it. It still won't idle right. Pigtail wire to ground the breaker plate is
in good shape. It never stalls, just has a very jittery idle. Also, it starts like
new. I'm thinking vacuum advance may be failed. (Dual system)?
Answer: We would first do a compression check on the engine. The piston
rings could possibly be frozen to the piston as a result of sitting for 5 years
without running. You may also have a valve hanging up. Vacuum leaks are also a possibility.
Question: 2004 Chevrolet Monte Carlo mileage: 79,000. When the car is
cold and I start it the idle goes to 2000 rpm and slowly drops to around 800 rpm
then surges back and forth. It also seems to be skipping. If I let it sit for 3
or 4 minutes the service engine soon light comes on but if I just touch the gas
it goes off. I took it to be repaired but they couldn't find any computer codes
so they cleaned and rebuilt the throttle body but it didn't help. I brought it back
two more times and they replaced the 0� sensor and the EGR valve and the problem
is still there. It runs fine once it's warmed up.
Answer: We suspect a faulty idle speed motor. If not done recently, a
major tune up, including plug wires is in order here.
Question: 2004 Mitsubishi Lancer: 70,000. Keep in mind
I am a car amateur, the kind that many mechanics prey on. When I start the
car, it takes a couple of extra seconds for the idle to go down. When I am
driving the car it seems like I *MIGHT* have lost a little bit of power. Also,
when I come to a stoplight the idle will rev up a little then go down kind of like
this rrrrrrrRRRRRRRRRrrrrrrrrrrRRRRRRRRRrrrrrrrrRRRRRRRRRRrrrrr. What
could be the problem?
Answer: This is a difficult problem to detect because the
computer can not sense a malfunction, the vehicles computer system thinks everything
is ok. In reality what is happening is the electrical component inside the MAF sensor
becomes contaminated by air impurities. These containments imbed themselves to the
electrical component that senses the air flow causing the sensor to be slightly
off, but not enough to trigger the MIL (malfunction indicator lamp). Replace the
MAF sensor with a new. NOTE: (Mass Air Flow MAF sensor or Air Intake Sensor AIS,
depending on manufacturer. It does the same thing only with different names).
Question: 2001 Dodge Truck 1500 mileage: 72,000. If
you can successfully pinpoint this problem, you should be President. The problem
is rough idle. Service Engine Soon light comes on intermittently. We
have replaced the wires, plugs, throttle position sensor, and idle air control valve.
Performance improved (better acceleration, surging stopped), but the idle problem
persists. Have checked for vacuum leaks, maybe not successfully...?
Should we bother with the oxygen sensor? EGR valve? PCV?
Auughh! Can you help? Mechanics in our area have been no help.
Answer: This is a difficult problem to detect because the
computer can not sense a malfunction, the vehicles computer system thinks everything
is ok. In reality what is happening is the electrical component inside the MAF sensor
becomes contaminated by air impurities. These containments imbed themselves to the
electrical component that senses the air flow causing the sensor to be slightly
off, but not enough to trigger the MIL (malfunction indicator lamp). Replace the
MAF sensor with a new. NOTE: (Mass Air Flow MAF sensor or Air Intake Sensor AIS,
depending on manufacturer. It does the same thing only with different names).
Question: 1998 Honda CRX mileage: 116,000. Hello,
the car sat for four months because it needed a head gasket replaced. Therefore,
I did the repair and now it does not want stay running as if it is starving for
gas. If you keep working the gas pedal, it will just idle. If you spray
carburetor cleaner in the carburetor it will run?
Answer: From what you describe, it sounds like you need
a set of fuel injectors.
Question: 1992 Plymouth Acclaim 2.5 mileage: 78,000.
Hi, my Acclaim 2.5L idles around 1200 RPM when cold but after a few miles on the
highway it starts to idle at 2000-2500 RPM. The computer gave me fault codes
about the TPS (throttle plate sensor) and the idle speed motor, so I changed these
two parts and the problem is still not fixed. The idle problem seems to get
better when I let the engine heat up. Any ideas on this problem?
Answer: Our guess would have been the throttle plate
sensor or the idle speed motor also. The next sensors to try would be the
oxygen and coolant temperature sensors.
Question: 2002 Toyota Pick up mileage: 67,000. I am
simply amazed with these trucks, mine still runs like a top, however: I live in
California and the EPA regulations here are very strict. All of my emissions
passed with flying colors but I failed the test because my AC idle up is always
activated (according to the diagnostics I performed with the engine "short circuit"
check engine light [code 11]. Air works great but the idle goes down instead
of up when I start the AC. How can I fix the AC Idle up module or disable the AC
to pass the smog test? I can only get to 9 degrees BTDC and I need it
to go to 3-5 BTDC at idle. I just had a timing chain installed and it is installed
correctly. Where is the AC idle up computer and do I have to replace it?
The temperature does get hotter than normal in mountain climbs or long hauls, but
I suspect it may be because the timing may be to retarded at high speeds.
Please advise.
Answer: You should double check the alignment marks
on the timing belt sprockets. You should be able to set the AC idle speed
with the adjustment screen on the bypass solenoid.
Question: 1999 Chevrolet 1500 mileage: 135,000. My car
is in very good condition; however, it has developed a rough idle upon coming to
a complete stop. The tachometer oscillates between 200 Rpms to approximately
1300 Rpms. If I don't even off the idle by giving it a little gas, the engine
stalls. How and where do I adjust the idle? Thank you in advance
for your help.
Answer: The idle speed is controlled by the computer.
Your car may be ready for a major tune-up including spark plugs, plug wires, distributor
cap, rotor, fuel filter and air filter. Also, perform a fuel pump pressure
test. Clean fuel injection system including throttle bore, idle speed control
motor and passages. If problem still exists, scan computer for trouble codes.
Question: 1999 VW Golf mileage: 130,000. I am experiencing
a problem with the warm up phase. The engine will increase to 2500-3000 revs
as it warms up. It will then stay at this level for anything up to 30 minutes
and then drop back to normal (suddenly). For no apparent recent the engine
will now and again suddenly start racing again only to drop back to normal just
as suddenly. Any ideas? I wonder if the culprit is the Stage II vacuum
delay. If you have no probable solution, I would be happy with a list of the
units or components that could be responsible.
Answer: First check the Mass Air Flow Sensor then check the thermo time
switch for cold start injector, fuel injection temperature sensor.
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