Reasons for Rough Idle?

SubaSteevo · #1 01-08-2003, 09:25 PM

I already searched the forums and got some answers, but I was hoping someone may know something that I couldn't find.

So here's the story...
I'm driving home from work and I notice my check engine light is on, so I pull into a parking lot and check everything out. The car is idleing rough/funny (shaking) but everything looks ok so I head home. At home I notice that the rpm's are going up and down (between 750-250). While this happens my headlights dim and get then bright again. The belts seem to sound like they slow down and then speed up again too. There is a slight whistling sound from the engine bay (drivers side I think) as well as a slight clunking from the passenger side (just the exhaust...I think anyway) and the car stalled out on me. I checked all the hoses and everything looks OK. I take it for a spin and the check engine light goes out, the car rides normal. I leave it parked for a while, then the symptoms come back (except the light stayed off). I stuck some STP in the gas tank thinking it might be water in my gas, but it didn't help any.

I have searched the forums and have found similar symptoms. I have printed the code diagnosis and will run it tomorrow. Possible solutions I have found include cleaning the throttle body or MAF, and replacing the fuel pump or O2 sensors. Any other possible solutions? Now for the "I'm still a kid and don't know anything about cars" questions...where/what are the MAF and throttle body and how would I go about cleaning them (pics are appreciated)? Any other info/solutions about this problem would also be greatly appreciated.

P.S. I'm hoping this will be "the post" for people who have this problem and will require less searching for other members in the future, so any info you have to add should go to good use.

DavieGravy · #2 01-09-2003, 04:52 AM

To help you narrow it down, I have this problem, my throttle body is clean, and I've just replaced my fuel filter. I've heard about the knock sensor going bad and causing similar problems.

By the way, take a look at the thin hose for the cruise control. It's right up against the firewall on the top and goes into a little cylindar by the brake fluid resevoir. It has a tendency to get knocked loose and has caused members here to have idle problems. Although in my situation this isn't the case.

SubaSteevo · #3 01-09-2003, 05:54 AM

This morning I pushed in all the wires just to make sure. The wire you described may have been a little loose. I also installed a new air filter (not to fix this, mine was just getting to be a little dirty). So far there have been no problems

, I am still curious as to how to clean the throttle body though. Thanks Davie.

SubaSteevo · #4 01-09-2003, 05:23 PM

My car started acting funny today so I cleaned out the throttle body after I found that someone had posted a mini how-to a while ago (aredubjay I believe). Car runs great now *knock*knock*

Aredubjay · #5 01-10-2003, 10:47 AM

For future reference, print this out. It's the General Trouble Shooting Chart from the 92 service manual.

#6 01-10-2003, 03:47 PM

if it happens again from time to time, check the starter coil. When mine went bad it caused rough idle, since once cylinder wasnt working. when you got into the low rpms 500 or so you could actually hear one of the cylinders being left out of the engine cycle.

DavieGravy · #7 01-10-2003, 04:17 PM

when that happens, how noticable is it?

#8 01-10-2003, 04:39 PM

to me it sounds like your belts could be loose or slipping. when my PS belt was slipping, I got warning lights now and then, and the headlights would noticably fluctuate.. when my AC belt started slipping, the car would squeal like a pig and then stall on me.. try tightening both belts down and see what happens..

-adam

#9 01-10-2003, 05:12 PM

I had all my belts and the spark plugs replaced, and my idle is almost silky smooth now. If you really really feel for it you can notice a bit of a knock but it's hard to tell.

solarsvx · #10 01-10-2003, 05:37 PM

mine is also idling rough..

but i think its due to the oil change thatt is due => i run synthetic should be okay

it might need new spark plugs but suposely was changed at 70k
pcv vavlve was changed recently also
bad knock sensor maybe???

not shure if the fuel pump was done im thinking it was but could be a solution

bad MAF reading??? could be a issue also.

i just changed the TPS sesor recomend bye the tranmsions guy.

the IAS or idle air stabilizer or whatever its called for a subaru works fine..

rough idling can be many things, =<

ohh bad motor mounts also .

Aredubjay · #11 01-11-2003, 12:42 AM

Quote:

Originally posted by DavieGravy
when that happens, how noticable is it?

I've never had it happen to me, but, over the past three years that I've been involved in these forums, when a coil completely goes out, the car shakes like it's going to fall apart. Sometimes, if the boot on the spark plug is cracked, you could get a bit of a rough idle also. Unfortunately, I don't think there's a part number for just the boot, however, someone found some spark plug wire boots (you have to by the plug wire set and use the distributor end of the boot) that serve. I can't remember whether that was posted on the Yahoo board, or this one. You could search both for "Spark Plug Wires" (shouldn't be too many posts, since we don't really have them) for the possible solution.

DavieGravy · #12 01-11-2003, 09:31 AM

Quote:

Originally posted by Aredubjay

I've never had it happen to me, but, over the past three years that I've been involved in these forums, when a coil completely goes out, the car shakes like it's going to fall apart. Sometimes, if the boot on the spark plug is cracked, you could get a bit of a rough idle also. Unfortunately, I don't think there's a part number for just the boot, however, someone found some spark plug wire boots (you have to by the plug wire set and use the distributor end of the boot) that serve. I can't remember whether that was posted on the Yahoo board, or this one. You could search both for "Spark Plug Wires" (shouldn't be too many posts, since we don't really have them) for the possible solution.

Thanks. I didn't want to be running on less than 6 cylinders without realizing it as this can ruin the catalytic converters. Although I think mine's on its way out anyway.

Landshark · #13 01-11-2003, 09:43 AM

if the coil is replaced, is the spark plug boot in effect replaced, too? i've never seen a coil pack off the car and was wondering if the boot was attached to the coil pack or a seperate part.

#14 01-11-2003, 04:01 PM

its pretty noticeable, your car would be shaking horribly at low rpms but smooth out at 1000-2000+ rpms, but sound kinda wierd. If you go to the back of the car and listen to the tailpipes, the car would sound more like a quiet idling outboard engine when it should sound smooth, or not much of a sound at all.

#15 06-30-2003, 03:46 AM

Quote:

Originally posted by I_Alcyone_I
if it happens again from time to time, check the starter coil. When mine went bad it caused rough idle, since once cylinder wasnt working.

Hi Everyone.

Anybody can tell me where to look for that starter coil? I happened to bump into the same engine idle shaking problem.

Cheers, RSK