Erratic Idle!! Please help

[shayrgob]

Ive had this erratic idle for about a few months. It only happens in the morning when cold. It stays at around 500 and seems like its about to die and then it jumps to 2000 for a second and comes back down. I have searched for this in the archives but i believe my problem is different. I checked the IAC and it looked brand new. I checked the MAS, and it looked very clean. I just checked my air filter and its a little dirty, but it shouldnt be causing this. A few weeks ago i had a check engine light pop up and i took it to autozone and the guy said it was a fuel delivery problem. So I directly assumed that it was probably a fuel fliter, but the guy said to just run a fuel cleaner through the system. So i did that, but the problem persisted. Could there be a problem w/ the spark plugs, Or should i change my fuel filter first and then take it from there? thanks

 

[mrboyle]

It could be a number of things. The IAC is the most common problem. Did you try cleaning it? It may look clean but there is a lot of the valve that can't be seen by just looking at it.
As for the filter, if it has been less than 30K (and you don't run cheap gas) since you changed it last, it should be fine. Anything over 30K I'd go ahead and change it (I doubt its the problem though).
Now, about the code. What was it?
NEVER believe what one of the idiots at AutoShaft tell you the "problem" is. Get them to write down the code number and erase it. Thats it! Most of the employees at thoes places know absolutley nothing about how to repair a vehicle, only what they have been told. Take the code info you are given and use either your repair manual or one of the many inernet sources (such as here) and figue out what the code means. I can tell you from experience that over 50% of thes codes you get have no direct relation to the code set.
For example, say you get a code P0171 Sytem Adaptive Fuel too Lean (bank one). Most people would assume that this means the vehicle is running lean, when in fact the most common problem is excessive fuel. The code means that the Adaptive Fuel has leaned the fuel to its mininimum amount, yet the vehicle is still running rich. You need to know what you are dealing with, before you can fix the problem.

NOTE: I'm not trying to be rude and tell you that you don't know what you are doing. What I'm trying to say is that there is a lot more to diagnosing some probems than most people think. It typically takes a lot of detective work and experience doesn't hurt either.

 

[shayrgob]

well, i dont have the code b/c it has been erased. So the only way i can get that is if it comes back. So what should i do? thanks

 

[nserafini]

For the $10 it costs, why not put a new fuel filter in anyway ... ( Depending on the miles on the old one )

Can't hurt, right ?

 

[mrboyle]

The first thing I'd do is clean the IAC and see if it will fix the problem. I wouldn't worry about the code if it doesn't come back. If the code comes back, follow my previous recomendations.

 

[nospeed_!2]

I have the same sort of problem. When i am sitting in traffic for about 2 mins maybe less. the rpm's tend to die then jump a few times, the car shakes and then if i dont give it some gas it stalls. im working on getting the code reader in but i dont have access to one currently. i also noticed that the rpms spaz when i am coasting for a while, but this is minor compare to the times when i am idleing. I can use all the help possible, thanks.

 

[checkedout]

any of you guys solve this? Mine started doing it last night. Mike, if it throws a code today I'll get it read but in your example, if it is a P0171, what would be the most likely defective part?

 

[Billy177]

chances are it is your intake manifold orings leaking get them fixed under recall

 

[checkedout]

I guess anything is possible but they were replaced about 7K ago when I replaced the heads.

 

[Billy177]

i thought you had a 98

 

[checkedout]

That's ok. At leats it brought it back to the top.

 

[checkedout]

surely you fixed it by now?

 

[ton_e_montana]

I am having the same problem with my girlfiends 98 SOHC. It threw PO171 and PO174(lean bank 1 and lean bank2). I have cleaned the IAC and am now going to replace the TPS tomorrow.....we'll see.

 

[ton_e_montana]

was also told to clean the MAF and it could also be the manifold o-rings. This problem seems to be a pretty broad troubleshoot so I am going cheap/easiest and on up.