Rough Idle And No Codes

[scatgo]

My 2002 with 89000 miles on it started to run rough about a month ago.
I changed the plugs and wires but still have the same problem. Used a gas treatment twice but nada. The funny thing is NO CODES!?! I had a Nissan that picked up a misfire on one cylinder that I didn't even know about but my PT idles like crap and the PCM wont give a hint as to what the problem is. So what might be cause the idle problem and whats up with the PCM?

Thanks for any help.

[CREWZIN]

Originally Posted by scatgo

So what might be cause the idle problem and whats up with the PCM?

Thanks for any help.

Not sure of your question. The PCM doesn't give a code for everything that ever happens. Some sensor somewhere has to see a problem before sending a signal to the PCM to set a code and apparently whatever you problem is, is not doing that.

Some owners have had a dirty/malfunctioning IAC (Idle Air Controller) which would cause a rough idle. It can be taken off and cleaned or just replaced.

[scatgo]

Ill look into the IAC. As far as the PCM I thought a rough idle wold set off a code for a misfire because it is running so rough. Is there any way to test the IAC?

Thanks

[CREWZIN]

Originally Posted by scatgo

Ill look into the IAC. As far as the PCM I thought a rough idle would set off a code for a misfire because it is running so rough.

Thanks

Yes, IF there's a misfire. Your rough idle could be caused by numerous other conditions.

From PT Cruizer.com:

All Chrysler vehicles with fuel injection have had some form of "error checking." In many older vehicles, a person could easily turn the key back and forth a few times to get a two-digit code. With the PT Cruiser, a longer code seems to be used. In addition, as with all vehicles sold in the United States, the system is OBDC3 compatible, so that a standard diagnostic device can be plugged into a standard jack to get computer codes.

When some problems are found, the computer lights up the "engine light;" others are ignored until a mechanic asks for them. The "engine light" stays on when a serious emissions or engine problem is found, until the code is erased.

Chrysler vehicles have a "limp in" mode which reverts to a pre-programmed "guessing map" for timing, fuel delivery, etc. when a critical sensor fails. Those who have been in other cars when their oxygen sensor failed can feel grateful for this feature, though it can be confusing - for example, in some (maybe all) models, the automatic transmission is limited to second gear! The engine light also turns itself on for two seconds every time the car is started so you will know the bulb still works.

[disneypunk]

hello i have the answer that noone has i am 17yrs tech and this one stumped me misfire cyl 4 only at idle #1 the intakes (lower) are famous for leaking so it would niot hurt to purchase 1 (approx. $100) once the intake is off you can clean the intake valves just be careful not to bent them or get the carbon in the cyl. with out being able to blow it out #2 the egr valve is leaking thru the diaphram causing a massive vaccum leak which can only be seen if a scanner is hooked up and feul trim is being watched in real time once you spray carb cleaner into the diaphram the trim will drop into the low minus like -22% #3 not only is the egr leaking but the egr tube gasket is also leaking ($1.95 from dealer) this occurs because of the removal of the upper intake to replace the plugs the egr valve is sold with the back pressure transducer from the dealer for about $136 list again it took me a lonfg time to figure this out so i felt the nned to share it with everyone since everyone thinks it is the plugs and wires good luck and spread the word-lenny

[disneypunk]

hey guys the egr gasket i am talking about is the one from the tube to the egr valve this will also get rid of that annoying spark knock and rattle going up hills. and yes there maybe some cars that have other problems but i will garantee that this will help 98% of the people out there and again i did every test down to an injector balance test which is approx. 30 psi @10 milliseconds -lenny

[CREWZIN]

Lenny,

Thanks for your input. Here's a few periods, please use them ........ It's hard to read what your saying without them; spell check wouldn't hurt either.

From what I understand your saying that if you get a code for a miss-fire on cylinder #4 at idle your saying: replace the lower intake, clean the intake valves, and replace the EGR and tube gasket, all for $331.00.

Thanks