Answer: It sounds like it is time for a major tune up including: spark plugs, spark plug wires (if equipped), fuel injection service, clean the throttle bore, idle air passages and idle air control motor. Also replace the fuel filter and air filter.

Question: 1999 Chevy 1500 mileage: 120,000. My truck seams to keep idling high and low when it is cold. When it warms up it gets a little better. The check engine light keeps coming on and keeps giving me the codes to change my oxygen censor and code 44 lean mixture. I have changed both and it keeps giving me these codes. What could be my problem?

Answer: Check the fuel pressure as it may be low caused by a plugged filter or a weak fuel pump.

Question: 2003 Chevrolet Corvette mileage: 55,000. Recently, the car has not been running up to par. It started off with the idle speed at low Rpms, {500-600) and would surge up to around 900-1000 and back down. After driving the car for a few days, the problem became worse and would stall when stopping in traffic. However, the car ran fine at normal driving speed. {45-65 mph} After a few more times on the road. Since that time, I have replaced the O2 sensor. Also, I have made inspections to the air management and vacuum emission hoses. So far, I cannot locate any leaks. Car is super clean. I am still having the problem of getting the car to idle and after the car reaches normal operating temperature. It will repeat even after re-setting the computer. I have scanned the main PCM but no codes what could be wrong?

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: 2002 Ford Explore mileage: 70,000. I've had the same intermittent problem for about 3 years, have never totally nailed the fix. Now at least it's getting worse, which as far as I'm concerned is a good thing-- at least it's consistent. Here are the long-term conditions and symptoms: runs great, except under 3 conditions-- 1) start and stop traffic 2) city driving in the heat or 3) driving under a load at the end of a long drive. The symptoms for 1) and 2) are poor idling, loss of power, and stalling and for 3) sudden, severe loss of power and stalling. In either case, it may not start for some time (which under these conditions can be extremely stressful). The problem is usually preceded by a gasoline smell or more often, a distinctive, rotten egg odor different from either gasoline or exhaust. Now, it stalls after even a short city drive. I had the catalytic converter checked today to see if it was plugged-- it wasn't-- but the mechanic made the note that there was a lot of unburned fuel in the exhaust-- he could smell it.

He also mentioned a lot of carbon buildup in the exhaust system. Repairs I've made include fuel pump/filter, plugs, and electronic ignition, and the best results I've had lasted about a year due to the replacement of EKG, sensors & hoses, which at the time were packed with carbon. The mechanic on this job mentioned at the time that he was unable to adjust the idle properly-- it was set as low as possible yet idled slightly fast. Any suggestions about the root of the problem or how to get at it? Thanks.

Answer: The first think we would check would be an fuel pressure regulator that has failed and is dumping fuel into the intake. This would account for the rotten egg odor that you noticed.

Question: 2002 Pontiac Grand Prix mileage: 30,000. The car has an idle problem. It is somewhat intermittent. When first started it almost always idles well. When the engine is up to, half the normal operating temperature through normal temperature the idle becomes slightly rough. If the brake pedal is partially released and the car begins to move forward it feels jerky as if there is a miss, the car never stalls but sometimes the engine speed becomes erratic and it feels as if it lopes. The tach will fluctuate between 1200 and about 700 rpm when the car is idling at its worst (though it rarely gets that bad).

When I pull away it accelerates smoothly and powerfully, at the next stoplight the idle is fine. After that, it usually happens all the time at a stop but rarely is the miss very pronounced, yet always present. Fuel pressure is fine the spark plugs are fairly new and not fouled. Also sometimes at cruising speeds of about 55 mph going up a hill in top gear {automatic w/overdrive trans) under light acceleration the sane kind of slightly jerky "miss" is felt. There are no trouble codes set ever. The engine does not burn any oil. It has a new catalytic converter.

Answer: It sounds like it is time for a major tune up including: spark plugs, spark plug wires (if equipped), fuel injection service, clean the throttle bore, idle air passages and idle air control motor. Also replace the fuel filter and air filter.

Question: 2002 Toyota Camry mileage: 72,000. Vehicle towed into my shop idles really rough; I replaced cap, wires, rotor, and plugs. Still idles rough, replaced timing belt, fuel filter, and injectors, fuel pressure o.k. Replaced dist with good one still runs rough. Compression at 175 all cylinders. No codes, replaced igniter, checked all grounds ok removed both o2 sensors to check for backpressure still idles rough. ECM was replaced at dealer. They were not able to figure it out either. I checked for vacuum leaks externally non-found. No vacuum inside valve cover either this has me and my mechanics stumped. Customer states vehicle was running fine, and then went to start it the next morning when it started running rough. I also checked injector signal at all injectors' waveform o.k. all data from scanner normal, will not accelerate at idle, bogs unless I spray carburetor spray rpm will pick up and run smooth above 1800 rpm and stay running smooth even after I stop spraying carburetor spray. But when you let it go below 1800 rpm. It starts running rough again. This car is kicking my butt. I would really like some help.

Answer: Check the EGR valve to make sure it is closed at idle and operating properly. In addition, check the fuel injector flow. Even though you checked the injector waveform, the injector nozzle may still be faulty. Also perform a cylinder leak down test, you may have an intake valve that is leaking.

Question: 1999 Dodge Intrepid mileage: 107,000. Hi, I've got 2 problems, 1 is almost similar in your FAQ, but not quite: FAQ:"1990 Dodge Ram 250 4x 5.2 mileage: 140000. Truck will start and run fine then die going down the road and will not start. The next day it will start and run fine for a while and die again. I replaced the fuel filter and cam-sensing unit. Answer: It appears you may have a faulty fuel pump." Problem 1: about 2-3 min after start, a soft knock may be heard, detectable inside the car with windows up. You have to listen real hard to figure out where it is coming from with the opened hood. This never seemed to be a problem, even though it is constant, sometimes annoying and its frequency elevates in exact proportion with acceleration. Oil level OK. Nobody could tell what might be wrong, so I just tried to forget about it. I never had any problems with engine or any other "major" stuff. Problem 2: Today stopped at the red light, oil sign flashed for a second and engine died. I was able to start it once again immediately, but it would not run idle, unless I increase rpm from 450-500 to 700. At 700 rpm engine was running idle for 6 hours - not a hiccup. Hot start-no problem, but it wants the same 700-rpm or more to keep itself alive. Slight unusual vibration of the engine can be seen. Questions: could you give me at least a probability of what might be wrong? Would you recommend to take the car to the dealership or I still have chance to save some $$ taking alternative route?

Answer: The engine noise, it is impossible for us to help you here without listening to the engine ourselves. As for your idling problem, check all the vacuum hoses and intake manifold gaskets as you might have a slight vacuum leak somewhere. In addition, check the idle speed control motor to make sure it is operating properly. If all checks out okay, scan the computer for fault codes.

Question: 2002 Audi A4 mileage: 59,000.  When I start the car in the morning or afternoon after work, the engine idles very rough for a few seconds before going to normal.  Sometimes the RPM will fluctuate from very high to very low after starting.  Sometimes when switching gears (5 speed manual) the RPM remains high and doesn't drop when easing off the gas.  After driving for a length of time (about 45 minutes) and I stop for about 5 minutes the car will not start until after about 30 minutes, and will continue to run erratic.  I took it to the Audi deal here in Saudi Arabia and they said they replaced the air filter, regulator (part no.  VW034 133 482) and adjusted output idling, but after about a week it was back doing the same thing.  I would appreciate any advice as to what might be the problem.

Answer: Scan the computer for fault codes.  Also, check the oxygen sensor and coolant sensors.