slow idle/ stalling; need help troubleshooting

[Cutehumor]

Hi everyone

My beloved 92 mirage 1.5 liter has a slow/rough idle whenver I come to a stoplight and after start up. Driving the car at various speeds have no problem at all. This slow/rough idle didn't show up until I replaced the lower and top radiator hoses, flushed the coolant out. I did have the battery disconnected for two days while I did the maintence. I did bung up the maintence a bit, the rubber hose in the coolant reservior, I forgot to reattach it.

but my car never ran hot. I discovered that two days later after seeing the radiator was empty when checking out the idle problem. After scouring the internet for information, the coolant temp sensor could cause the rought idle. But everywhere I look, everyone says the idle air control valve/throttle plate is carboned up. I just got done using carburetor cleaner on the throttle plate and scrubbed out some carbon. I disconnected my battery again hoping to reset the ECU. I can't find the idle air control valve anywhere! anyone have a clue? Anything else I should look for? I don't want to throw money at parts. I've read that It could be TPS ($130), plug wires, oxygen sensor, IACV ($220), throttle plate.

If it means anything, I have the same rough idle when the Air conditioning is on. It's done that for years. now I have a rough idle at stoplights with the a/c is on or not

 

[RussellA]

Being that this rough idle showed up after you changed the radiator hoses, I would carefully inspect all vacuum hose lines to make sure none are pulled lose or broken. I often have bad luck at breaking one thing when fixing another. Easy to pull loose a vacuum hose or have it crack if the rubber has gotten brittle. Given it's a 92, there is a good chance alot of the vacuum hose has gotten brittle.

 

[moribundman]

Cutehumor,
It looks like you are aware of most or all possible sources of poor idle. Like Russel said, a vacuum leak can cause those symptoms, too, so check all vac hoses (throttle body gasket, too). I'd also make sure the spark plugs and wires (ignition coils, too) are okay. Check also all electric connections.
I don't know if your car has an ICV, but it should be close to the throttle body and/or intake manifold. Does your car have a MAF sensor? If that is dirty or defective, then the engine won't idle/run well.

 

[DJStillman]

How about a diagnostic system? Most cars by 92 had some form of on board computer with an area to check for errors. Instead of guessing, why not just ask the car? A repair manual should have the code information, such as where the setup is, how to access it, and what the results mean.

Good luck.

 

[moribundman]

If the Mirage's diagnostic system is anything like my Audi's, then you need either to pay the dealer something like $70 to pull the codes, or you have to get a compatible scanner and software, if available.

Gone are the days of simply counting a blinking error light to figure out a code...

[ August 14, 2003, 10:45 PM: Message edited by: moribundman ]

 

[Cutehumor]

I got new news. I drove the car about 30 miles since the throttle plate cleaning. When I first fired up the car, it cranked but didn't start. Second time I cranked the car, it started but it was pretty loud like an explosion (maybe some residue carburetor cleaner in the throttle body). the idle was really high then settled down to a normal speed. I guess the ECU had to relearn the idle speed. I let the car idle for 3-4 minutes and drove off gently. When I take the vehicle to a stop sign or stoplight, the vibration isn't there anymore or the idle isn't weak. The idle sounds fast now, but all I did was scrub out some carbon around the throttle plate. Maybe the fast idle I'm hearing is the natural idle? It's like if you hear a slow idle for a year, it takes awhile to get used to the actual idle of the car? hopefully the symptoms won't return, I read that an erratic idle can kill your catalic converter. Thanks to everyone who gave me advice.

RussellA,
I did check all the vacumm hoses, I didn't see any loose or broken hoses. Some have gotten hard though that they won't pull off. Thanks for helping a poor college student. I wish some of my friends were into cars like I am. Everything I've learned have either come from the internet or my Haynes manual. This is a great site and I have learned alot.

[ August 15, 2003, 09:47 AM: Message edited by: Cutehumor ]

 

[Cutehumor]

quote:

---

Originally posted by moribundman:
Cutehumor,
I'd also make sure the spark plugs and wires (ignition coils, too) are okay. Check also all electric connections.
I don't know if your car has an ICV, but it should be close to the throttle body and/or intake manifold. Does your car have a MAF sensor? If that is dirty or defective, then the engine won't idle/run well.

---

Moribundman,
I think I was looking in the wrong place. I read the the ICV is butterfly shaped? I did look at the MAF sensor I found something interesting. The end of it has a bunch of small holes in it, there was some type of glue at the end of it. not alot though, I don't know if that is normal? I was running a KN air filter for the past 8k miles too, I was afraid it was letting in too much dirt from all I've read about them. I swiched to a paper Fram air filter just in case.

[ August 15, 2003, 09:45 AM: Message edited by: Cutehumor ]

 

[Bdiddy]

If you've had a K&N airfilter on there, it's possible that the oil used on the filter could have fouled the MAF, at least if the setup is anything like on Ford Tbirds... It'd be a good idea to get some electrical contact cleaner (available at Radioshack and elsewhere) and clean your MAF if possible. This is good to do as they get dirty over time anyway.

 

[moribundman]

Cutehumor,

I have no idea how the ICV looks on your car. On my Audi it's a pintle valve (not a butterfly valve) that is actuated by a stepper motor via the ECU. My ICV is contained in a cylindrical housing, roughly 5 inches tall. Cars that don't have an idle control valve, may have a motorized throttle body. The ECU actuates the butterfly valve(s) in the throttle directly to compensate for the need for more or less air.

I'm also not sure how your MAF sensor looks. I'm aware of two different setups. One is a simple wire with a thermistor, the other type uses a flat thermistor. Both tend to become dirty, so cleaning is a good idea. Electronic cleaner might leave some oily residue (The one I got from Radio Shock did), so I'd still rinse the sensor wire in isopropyl alcohol.

Glad the idle got better!

 

[Silk]

I would say you just had an air lock in the throttle body/idle control motor.These are small coolant pipes and when you drain the system you will have to bleed the air out - otherwise you get an eratic idle...while you were playing around with other things the air lock cleared and idle control returned to normal.

 

[NutBuster]

It's a simple problem...seen it many times. It's just a gummed up throttle body. Hosing it with the proper cleaner usually will clear up a low idle problem. It's not typically caused by poor air filtration, but by unburned fuel vapors that build up over time. Each time you shut the car off, any minute amount of fuel that didn't make it to the combustion process will vaporize on the hot intake valves and eventually leave a dark film on your intake parts all the way up to the throttle body...this phenomenon is generally the reason you get sticky injectors as well.

There's no real "cure" for the problem, just clean the t-body every couple years or so depending on your driving habits. If you've got the time, just take the thing off and use a soft toothbrush on it.

in my experience, some cars are more prone to this problem than others. I saw it happen with many Mitsu-chrysler 3.0 V6 engines back in the day. Simple fix though...made a lot of customers happy just knowing the simple solution!

 

[NutBuster]

Good Job, Cutehumor...

A throttle body cleaning should be a core part of any tune up, especially when a port injected engine is involved. Spread the word!

After being around cars my whole life, I'm happy that I retained some useful information

 

[Cutehumor]

quote:

---

Originally posted by NutBuster:
It's a simple problem...seen it many times. It's just a gummed up throttle body. Hosing it with the proper cleaner usually will clear up a low idle problem. It's not typically caused by poor air filtration, but by unburned fuel vapors that build up over time. Each time you shut the car off, any minute amount of fuel that didn't make it to the combustion process will vaporize on the hot intake valves and eventually leave a dark film on your intake parts all the way up to the throttle body...this phenomenon is generally the reason you get sticky injectors as well.

There's no real "cure" for the problem, just clean the t-body every couple years or so depending on your driving habits. If you've got the time, just take the thing off and use a soft toothbrush on it.

in my experience, some cars are more prone to this problem than others. I saw it happen with many Mitsu-chrysler 3.0 V6 engines back in the day. Simple fix though...made a lot of customers happy just knowing the simple solution!

---

I agree with ya nutbuster. I used a can of carburetor cleaner around the throttle plate and scrubbed the black gunk off with an old toothbrush at the top and bottom of the throttle plate. When I fired up the car, idle has been smooth for a week now. It only took a $.78 cent can of carburetor cleaner and an old toothbrush to fix it. How's that for cost effective?

only reason I attempted this first instead of "throwing parts" at it was because it was the cheapest fix to do. It worked!!

btw, I found a website that talked about the 3.0 mits-chrysler engine throttle plate cleaning.

[ August 22, 2003, 12:18 PM: Message edited by: Cutehumor ]