Very Low Idle on Warm Start

[bluesmoke91]

So I have a 96 Corolla with 78k miles. Runs great but has a rough idle. On a cold start it high idles just as it should. Once the engine gets to operating temp and I shut off the car for a few minutes or an hour or so, the car starts and immediately goes into a very low idle, I'd guess about 200 rpm maybe less. The vehicle shakes vigorously but never stalls out, giving it a little gas during idle will stop it. After that the car drives and idle fine, rough idle, but fine.

I cleaned the throttle body with no noticeable change. I do not know the last time the car had a tune up done so my plans are distributor cap, rotor, plugs, wires, air filter, oil change, and while I'm in there, replace the Idle Air Control and Pcv.

Anyone have any thoughts?

 

[Donabed Kopoian]

Do everything except the Idle Air Control, and run a tank of premium with fuel injector cleaner.

The IAC is working fine.

Chances are the tune-up will fix it (does a '96 even have a distributor?), because a weak spark can cause a rough idle.

Also, when a car warms up it takes over 3 hours for the engine to cool off, so when an engine is warmed up and you shut it off, then restart it again within an hour, skipping the closed-loop mode is perfectly normal.

 

[bluesmoke91]

Do everything except the Idle Air Control, and run a tank of premium with fuel injector cleaner.

The IAC is working fine.

Chances are the tune-up will fix it (does a '96 even have a distributor?), because a weak spark can cause a rough idle.

Also, when a car warms up it takes over 3 hours for the engine to cool off, so when an engine is warmed up and you shut it off, then restart it again within an hour, skipping the closed-loop mode is perfectly normal.

Yea my 96 has a distributor. I understand skipping the high idle is normal as the engine is still warm. What trips me out is how low of an idle it goes into. It never idles that low, only when turning it on while still warm.
I'll take your word and do a simple tune up. I'm leaning heavily on the IAC, but I'll save myself the trouble until after the tune up if things aren't better.

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[Scott O'Kashan]

So I have a 96 Corolla with 78k miles. Runs great but has a rough idle. On a cold start it high idles just as it should. Once the engine gets to operating temp and I shut off the car for a few minutes or an hour or so, the car starts and immediately goes into a very low idle, I'd guess about 200 rpm maybe less. The vehicle shakes vigorously but never stalls out, giving it a little gas during idle will stop it. After that the car drives and idle fine, rough idle, but fine.

I cleaned the throttle body with no noticeable change. I do not know the last time the car had a tune up done so my plans are distributor cap, rotor, plugs, wires, air filter, oil change, and while I'm in there, replace the Idle Air Control and Pcv.

Anyone have any thoughts?

Don't change any parts. That can get very expensive and frustrating with a trash can full of perfectly good parts that didn't need replacing and a lot less money in your wallet. There's absolutely no benefit to replacing parts if they don't need replacing, except for the discount auto parts stores who take your money. Further, just doing the parts replacement routine can introduce other problems into the picture, like poor quality parts that don't do their job well, or are defective, or are potentially installed incorrectly, etc. This opens a Pandora's box of problems that complicate diagnosing the original problem and can lead to a royal mess.

Instead, diagnose.

If the spark plugs or spark plug wires were at fault, the check engine light would have come on, showing a misfire. If that hasn't happened, then replacing the spark plugs and spark plug wires, distributor cap, etc., will not cure the problem the car is having. It will however make your wallet lighter.

1. Is the check engine light turning on? If so, do you know what the codes are?

2. Have you had your cars onboard computer scanned to look for any stored trouble codes? Discount auto parts stores like Advance Auto Parts will do this for you for free.

3. Have you removed the spark plugs to look at them and see what kind of shape they are in?

4. Have you looked closely at the spark plug wires to see what kind of shape they are in?

5. Have you looked at the air filter? To see if an air filter is in need of replacement, hold it u to a strong light and if you can't really see the light through it very well, it's in need of replacement.

6. What procedure did you use to clean the throttle body?

7. Are you the original owner of the car?

 

[bluesmoke91]

If the spark plugs or spark plug wires were at fault, the check engine light would have come on, showing a misfire. If that hasn't happened, then replacing the spark plugs and spark plug wires, distributor cap, etc., will not cure the problem the car is having. It will however make your wallet lighter.

1. Is the check engine light turning on? If so, do you know what the codes are?

2. Have you had your cars onboard computer scanned to look for any stored trouble codes? Discount auto parts stores like Advance Auto Parts will do this for you for free.

3. Have you removed the spark plugs to look at them and see what kind of shape they are in?

4. Have you looked closely at the spark plug wires to see what kind of shape they are in?

5. Have you looked at the air filter? To see if an air filter is in need of replacement, hold it u to a strong light and if you can't really see the light through it very well, it's in need of replacement.

6. What procedure did you use to clean the throttle body?

7. Are you the original owner of the car?

Plugs or caps that aren't sparking as strong as they should would not always set off codes. That's why we replace things as a mean of preventative maintenance. Why wait until things do go bad?

1-2. There is no CEL on and I did scan the vehicle for hard codes, nothing came up.

3. Have not checked my plugs. I'll need to wait until I'm at work later today to grab my plug socket.

4. The wires seem to be in good shape. Will probably still replace just for peace of mind knowing everything is new.

5. The air filter is just a tad dirty. I can get away with blowing it out but would rather buy a new one, again, for peace of mind.

6. I removed the intake box and tube. With a rag sprayed with brake cleaner, I wiped it all down. turned the throttle to open the flap and wiped inside as best I could. The plenum insides are plenty gunky, that might have something to do with it as well.

7. I am not the original owner. I have only had it for 80 miles, bought last week. A few other things the car needs are axle boot reclamps if the boots aren't torn, shocks all the way around, and a water pump bypass hose that's bulging between the clamps. The low idle is my only mechanical concern.

 

[Donabed Kopoian]

An intermittent random misfire doesn't always trigger a CEL, and weak spark can cause rough idles. You meed a good scanner or Torque software to check the misfire count. I'm not sure what the threshold is to trigger the CEL.

Replacing the plugs improved my idle and got me an extra 2 mpg.

Look at the plugs, and compare the look of the plug to an online table that can show WHY the plug looks that way.

 

[bluesmoke91]

An intermittent random misfire doesn't always trigger a CEL, and weak spark can cause rough idles. You meed a good scanner or Torque software to check the misfire count. I'm not sure what the threshold is to trigger the CEL.

Replacing the plugs improved my idle and got me an extra 2 mpg.

Look at the plugs, and compare the look of the plug to an online table that can show WHY the plug looks that way.

I agree on the random misfires and weak sparks not always triggering a CEL. I'll see if I can hook up my Snap On scanner once I get to work to check the misfire counts if there are any.

The vehicle has very low mileage for the age, so I would not doubt that it's running on original plugs.

 

[Donabed Kopoian]

Keep us posted.

And yeah, those 100,000 miles plugs never last that long. Changed mine in the Matrix at 60,000 and the electrodes were almost gone. Granted... I drive aggressively.

 

[Scott O'Kashan]

Plugs or caps that aren't sparking as strong as they should would not always set off codes. That's why we replace things as a mean of preventative maintenance. Why wait until things do go bad?

1-2. There is no CEL on and I did scan the vehicle for hard codes, nothing came up.

3. Have not checked my plugs. I'll need to wait until I'm at work later today to grab my plug socket.

4. The wires seem to be in good shape. Will probably still replace just for peace of mind knowing everything is new.

5. The air filter is just a tad dirty. I can get away with blowing it out but would rather buy a new one, again, for peace of mind.

6. I removed the intake box and tube. With a rag sprayed with brake cleaner, I wiped it all down. turned the throttle to open the flap and wiped inside as best I could. The plenum insides are plenty gunky, that might have something to do with it as well.

7. I am not the original owner. I have only had it for 80 miles, bought last week. A few other things the car needs are axle boot reclamps if the boots aren't torn, shocks all the way around, and a water pump bypass hose that's bulging between the clamps. The low idle is my only mechanical concern.

If worn out spark plugs are continually causing misfires it should turn on the check engine light.

So how did the spark plugs look?

No need or benefit in replacing spark plug wires that are in good shape. Original equipment spark plug wires tend to be very good quality and replacing them with an aftermarket wire might taking one step forward and two steps back.

If the air filter is fine, save your money and put it to better use on your car with something else. :thumbsup:

CV boot axle reclamps?

Your Corolla should have MacPherson struts in the front and shock absorbers on the back. When replacing the struts, a four wheel alignment will need to be performed.

Any updates on the low idle issue?

 

[bluesmoke91]

If worn out spark plugs are continually causing misfires it should turn on the check engine light.

So how did the spark plugs look?

No need or benefit in replacing spark plug wires that are in good shape. Original equipment spark plug wires tend to be very good quality and replacing them with an aftermarket wire might taking one step forward and two steps back.

If the air filter is fine, save your money and put it to better use on your car with something else. :thumbsup:

CV boot axle reclamps?

Your Corolla should have MacPherson struts in the front and shock absorbers on the back. When replacing the struts, a four wheel alignment will need to be performed.

Any updates on the low idle issue?

No updates yet. Drove my truck to work Thursday and Friday, spent the day yesterday at a theme park, also drove my truck. Today the issue is much worse. Now it won't stay running when cold unless i hold the gas. Once off the gas it shuts off. I hold the revs up a while to raise the engine temp and now the idle is constantly very low. It used to idle fine once slightly warm.

Yes, the axle boot clamps seem a little loose as I could see grease seeping from outside the clamps, not the boots themselves which leads me to believe that the boots are not torn, just not clamped enough. And yes the shock replacement will also have an alignment.

 

[Scott O'Kashan]

Hmmm...many Corolla's are noted for having intake manifold gasket leaks, which causes a vacuum leak, which could very well explain the symptoms your car is showing. If you take a spray bottle of water and spray along the edges of the intake manifold and around it while the engine is running and if the engine idle suddenly improves for a moment as you are spraying the water, you've found the vacuum leak. The water acts as a momentary barrier and helps the engine to run normally.

 

[bluesmoke91]

Hmmm...many Corolla's are noted for having intake manifold gasket leaks, which causes a vacuum leak, which could very well explain the symptoms your car is showing. If you take a spray bottle of water and spray along the edges of the intake manifold and around it while the engine is running and if the engine idle suddenly improves for a moment as you are spraying the water, you've found the vacuum leak. The water acts as a momentary barrier and helps the engine to run normally.

I want to try the water spray test but i cant seem to keep this thing running after it gets revved. Pretty much stalls as soon as the gas is let off. Pulled the plugs finally and they were looking rough so i replaced them. As expected, no change, but that's one less worry.

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[Scott O'Kashan]

Sure sounds like a vacuum leak.

 

[Donabed Kopoian]

Have a friend hold down the throttle for you while you spray around.

Another place to look is the brake booster. They age and eventually leak from repeated brake use.

 

[bluesmoke91]

Have a friend hold down the throttle for you while you spray around.

Another place to look is the brake booster. They age and eventually leak from repeated brake use.

Wouldn't a leaking brake booster cause a spongy brake pedal though? Brakes feel nice and tight, as they should.

Still leaning heavily on the IAC, my next step is cleaning that up with some carb cleaner. May have to wait until tuesday so i can bring some supplies and tools from work.

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[Donabed Kopoian]

No, that is a leaking brake master cylinder or leaking caliper. A leaking brake booster is a vacuum leak. It'll cause the brake pedal to be slightly stiffer than normal.

A broken IAC will either not rev up during warm-up or stay revved up at all times. If it gets loose, it will cause a vacuum leak like what you are describing, but the IAC itself is functioning fine.

IAC does NOT control idle when the engine is warmed up. The PCM does.

 

[bluesmoke91]

For those following, no updates. Been driving the corolla without issues. Still idles terribly low when started warm. The plug change softened up the idle while idling in drive at red lights and such.

Dropping money on my truck and tools is keeping me from the Corolla. Although i do have the replacement bypass hose for the water pump. Will hopefully swap that this weekend.

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[Donabed Kopoian]

Keep us updated. Good luck.

 

[bluesmoke91]

Short update.

Made it through summer without a single idle issue due to the warm weather. Now that temps are dropping, I'm having the same issue I did a few months back. All is well though, I will keep looking into my problem.

4 strut assemblies, all speaker replacement, and window tint planned in the next few weeks.