rough idle when warmed up

[Em cee]

hundy has been stumbling/missing at idle after warm up. runs great while cruising and accelerating.

• no check engine light but have replaced (2) coils in the past 6 or 7 mos.

• checked plugs and none were loose or oil-fouled

could it be an indicator that another coil is on its way out or dying a slow death?

wouldn't think it was a fueling issue since it runs so well under load but i did run a bottle of techron with 11 new gallons of 91 (that's the best stuff out here in CA) in it just to rule it out.

any insight would be appreciated, thanks fellas (and ladies).

 

[ponytl]

vacuum leak? maybe ? I use a propane plumbers torch (not lit) with gas running... move it around all the fittings... hoses ect... if/when the idle changes there is the problem... or at least the area it is in...

 

[Em cee]

*******update*******

looks like the techron is working and it mighta been a case of bad gas. took the old girl out and flogged her good with the new 91 fuel and it seems the 'italian tune up' did some magic. cautious about calling it fixed though till i run through the tank of gas. might be worth another bottle of techron for safe measure.

 

[2001LC]

How many miles and what year?
Any symptom before changing coils?
Would you mind posting your data on coils here: When to replace Ignition coils.

How'd gap look on plugs?
Even though it's running better, be a good time tuned once you run that gas out. Clean & check: Air filter, MAF, TB, PCV and most of all disconnect battery for 30 minutes to reset.

 

[Jackson Sanders]

I've been chasing this one for a while as well. I've tried cleaning the maf and throttle body, new plugs, disconnecting the battery, new motor mounts, sea foaming the intake, fixed all vacuum leaks, and ran fuel system cleaner in the gas... Although it is better than it was starting out, nothing has made it go away completely. My next step might be replacing the maf and o2 sensors if I can't come up with anything else to try.


Sent from my iPhone

 

[2001LC]

I've been chasing this one for a while as well. I've tried cleaning the maf and throttle body, new plugs, disconnecting the battery, new motor mounts, sea foaming the intake, fixed all vacuum leaks, and ran fuel system cleaner in the gas... Although it is better than it was starting out, nothing has made it go away completely. My next step might be replacing the maf and o2 sensors if I can't come up with anything else to try.

Sounds like you've done most common stuff. O2 and MAF should throw codes, so not likely the issue. I assume you've checked for stored codes.
Have you consider:
Fuel pressure quick test, pinch off return line (Edited: Pinching could damage line!) (DS hung on clip back of engine cover)
Having fuel injector cleaned & tested When to replace fuel injectors
Test and/or replace When to replace Ignition coils. In certain conditions worsen when hot.

 

[trizzo]

it seems the 'italian tune up' did some magic.

the italian tune up makes me laugh every time i read or say it. hilarious!

 

[Jackson Sanders]

I'll take a look at the fuel pressure, but the coils and fuel injectors both seem like a long shot in my opinion. Coils normally give codes when they go out as well, and it seems if there was an issue with the injectors it would affect the car in other conditions than just sitting at idle in drive.

I'm going to try seafoaming the intake and fuel system again I think, as it is cheap and easy. There was a ton of smoke that came out the first time I de-carbonized the intake system so maybe there is more crud that needs to be cleared out.

 

[2001LC]

Your right, codes will generally come up. But not always in the early stages, according to some post in the coil replacement thread. Dirty injector don't often show a code.

Good luck, let us know how it works out.

 

[Jackson Sanders]

I will keep you all updated. Thanks for the help LC!

 

[wolffo]

mine has done this for almost 40k miles, spent a bunch of money on it, gas pedal with TPS ($430), O2 sensors, sea foam, BG44, MAS air sensor, new plugs, air filter....same old thing
it feels like "fuel rail" to me, but you can throttle thru the problem spot and it runs like a top
however: the power is there, it passes emissions fine, gas mileage is there.....its just super freaking annoying.....and very non typical Toyota quality
it won't throw a code
and it won't break!

 

[Julian Stead]

I would try disconnecting the battery for 30 mins, then let idle for 15 mins without nothing on to reset, it can really help.

 

[Jackson Sanders]

I feel like mine has to be component related, for example something putting a heavier load on the motor when it is engaged. The reason being is it doesn't do it ALL the time, the idle is fine when it is hovering around ~700, then all of a sudden it drops down to ~600rpms and the whole vehicle starts shaking for a minute or two, then jumps back up to ~700 and so forth. I just can't figure out what it could be...

 

[wolffo]

like its cycling on the compressor for "defog" or air conditioner compressor type of "load"
yup, I would say mine is similar to that too
its annoying as all hell, but the vehicle drives great otherwise

 

[Em cee]

*******update*******

'rough idle when warm' has been back for a month or so. as others have described, roughness most evident while under light load. when idling at a stop light, will move shifter to N and 'stumbling' subsides. roughness during acceleration is most evident at low rpm range then smooths out during cruising

been waiting for it to throw a coil code but has not happened. really frustrating.

might try disconnecting the battery for 30, then let idle for 15 as Julian recommended and see what that does. will report back.

 

[fumanchu]

Search erratic idle. I changed my TPS. Fixed the idle issue.

 

[Em cee]

Fumanchu, thx for your post. I have no CEL, isn't this usually symptomatic of a failing or failed TPS?

 

[fumanchu]

I had no CEL either. I tried all the usual's...... My problem really reared its head when the ambient temps warmed up. Did it more in warmer weather than cold. Mine was the TPS. All is solved now, The TPS is touchy when you change it out, car went into limp mode after I changed it. Adjusted it some, cleared the code and got it to idle where I liked it and all is good. Should probably have it set up with a techstream to be sure of the setting though.
The TPS is a known failure in the early 100's ....FYI...

 

[Em cee]

Forgot to update this thread.

Replaced the TPS no change.

Removed and cleaned the TB no change.

R&R'd air filter hoping for a slight improvement no change.

Cleaned MAF no change.

Took it to the dealer and guess what? #3 coil. That's what I get for not doing the simple stuff 1st.