QuestionHi! Anothony,
Thanks a lot for the information. I took it to Tiresplus and they did a code read of the OBD and it came out to P0300 which is random misfire/multiple cylinder.
As mentioned I had taken to two mechanics, the first one was saying that as soon as he fixed a new CAT, the next reading he got from OBD was for O2 sensor and asked me to get it replaced..but I had changed the O2 sensor only 6 months back from TiresPlus. I took it back to TiresPlus for them to check the O2 sensor and replace it as it is still under warranty..As suspected they said there is nothing wrong with O2 sensor, the CEL is coming because of P0300 and I should change the spark plug, wires and the coils..
Now I was totally confused..on what can be the exact cause of random misfire, because I had changed the spark plugs, wires, CAT only a week back from the first mechanic
So I took it back to first mechanic who had changed the timing belt, alternator belts, air filter & also did tune up and CAT. He is saying that spark plugs & wires are good..and he didn't see constant problem with coils it was intermittent & that he can change the coils but then if it was the O2 sensor then after replacing the coils, I will not get any malfunction code with O2 sensor and I cannot go back to tireplus for changing that.
I am being tossed between two mechanics like a tennis ball..I wanted your advise or some direction on what could be the problem for low idling. Can these be one of the following reasons and what should I ask mechanic to check..specifically. Can they not do elimination method , looking at each of the probable cause and narrowing it down
a) Air filter ==> changed
b) Cat ==> Changed
c) Spark, wires ==> changed
d) Coils ==> Not changed
e) Bad timing ==> Mechanic says he has set the best timing possible. I started having this problem 1 week after I changed the timing belt, alternator belt and the air filter. While driving car is smooth except it coughs or jerks intermittently
f) EGR valve ==> Not checked or changed
g) O2 sensors ==> changed 6 months back
I will really appreciate your help on this as I am desparate. I have already spent 1000 bucks and there is not root cause for this problem which is a common problem. I can take it to a dealer, they charge 80 bucks for diagnostic..but not sure diagnostic will include the root cause or not and they might ask me to change everything possible.
Thanks in advnace
Shailesh
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Followup To
Question -
Hi! Anthony,
I have 2001 Mirage 1.8 L. Few days back after I changed my timing belt, alternator belts etc, the car started getting idling problem..it coughs, jerks and then stops mostly while it is idling. While driving also sometimes..when I release my foot from the pedal..it feels as if car is coughing and pushing back..when I leave it in idle..the engine noise goes up, then goes down, then goes up..then stalls , jerks violently and then stops
..I took it to the mechanic who had changed timing belt to see if it was something to do with ignition timing, they looked at it and said..timing as best as possible..I had a check engine light on at that time..which was indicating P0421 for a bad front cat. I used to get the check engine light on & off intermittently and was able to drive for 8 months without any problem..so they said it might be because of tune up..so I got the tune up done which included changing the spark plugs and the wires as part of the regular tune up..but I still had the problem so the mechanic said it is because of bad cat..I got the cat also changed but the idling problem still persists..now the mechanic is saying it might be due to bad O2 sensor as they got that code after they changed the CAT (today). At present Service engine soon light is not on (which should be if it was a bad O2) but the mechanic said ..they had reset it for test drive and will come back up after few miles ( I have already driven it for 20 miles..it has not come back yet)
I am fed up of going to mechanic's and I am not sure whom to believe.. Is it possible that a bad O2 can cause a idling problem.. I had changed the O2 6 months back from a different place and drove for 10,000 miles since then..
Is there anyway to pin point the exact cause without taking it to the mechanic for hit & trials..I don't want to go to a dealer because I have heard, they are always after ripping off (not sure how true that is)..I am amaetur with cars..so I myself don't have expereince or tools to do anything myself
Also I have seen your previous posts and you have recommended to take the car to either Autozone or PepBoys...As per your experience..are they good and honest..even if a little expensive..?
PS:- I am assuming that mechanic had cleaned the throttle body as part of the tune up
Answer -
Shailesh,
With most mechanics, I wouldn't assume they did anything unless it was in writing. For most tune-ups, cleaning the throttle body is not a common practice, though that's probably not causing your problem.
AutoZone does not offer repairs, but they do offer free services like battery checks, starter and alternator checks, and can read your car's computer for free when your check engine light comes on. Most Pepboys do offer repair services, but I typically only recommend them for items like tires, brakes, suspension, and exhaust. The big 'rip-off' at dealership mechanics is that the price on parts is very expensive, and labor cost is as well. I try to avoid them myself but for newer cars, it's the best place to take your car. They will have the most knowledge of your workings of your car.
Your average local mechanic has a general diagnostic code reader that can give a general answered when they hook it up to find out why your check engine light comes on. Some codes it'll just guess at because they are manufacturer specific, and only the dealerships' code readers will know for sure. But it can be difficult for anyone to pin point the exact cause. Your mechanic was right when he said your check engine light can come back on within a few miles. When dealing with emmissions problems, that's how the car's computer cycles the codes. It does not forget there's a problem, but won't turn on the light again until the cycle comes around again. Different systems on different cars take different amount of start ups and miles to show the light.
It sounds like your mechanic could be on the right track, but if you don't feel comfortable with his service anymore, by all means take your car to another mechanic. It pays to shop around for mechanics, so ask friends, family, and co-workers that know of any mechanics they recommend in your area.
Good luck!
AnswerShailesh,
Random misfires are difficult to diagnose because they are so random. Low idle can be adjusted by your mechanic, though this may be a procedure that he is not familiar with. Dealership mechanics will know how.
The check engine light (CEL) will come if it detects a problem with the ignition system, emmissions system, or a sensor. Unfortunately, a P0300 doesn't tell you which cylinder(s) has misfired, or why. The service manuals list these items as possible causes for this code to be thrown:
Faulty spark plugs or wires
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector(s)
Burned exhaust valve
Faulty catalytic converter(s)
Stuck/blocked EGR valve / passages
Faulty camshaft position sensor
Defective computer
You can check off the items that have already been replaced for your situation. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open. It could also be due to a clogged fuel filter, clogged fuel injector, or weak fuel pump. The mechanics are doing an elimination method to pinpoint the problem, but it's at the cost of time and money to you. Because they don't know exactly what's causing it, they are replacing the most common items in hopes they fix it. You can ask your mechanic(s) to check the items I've mentioned and maybe that will guide them to the exact cause.
Good luck!
