idle bouncing under 1000 and up (almost stalling)

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jokken

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just got done replacing the radiator in my 2000 LS. I was surprised no issue with my reassembly... I also got to replace most of the fluid in the hydraulic fan setup :Beer

the radiator was a bit of a job, it took me way too long, I was very happy the car started and just went, without any temperature issues, after I had it all apart for so long, and I was hung over this morning when I finished the job, in the rain...

but the elation was dampened a bit when I came to the light by my job. The same old issue happens: when coming to a stop (clutch in, in gear or not) the rpms drop well below 1000, the car almost stalls and then bounces the rpms back up to 1500, and then back down almost stalling again, repeat (with the AC on it does stall sometimes). This happens 80% of the time, i can sometimes, not always, get it to idle right if I jab the gas, and when the RPMs come back down they settle correctly around 1000.

This is coupled with another annoyance: about 50% of the time when coming to a stop if I don't press in the clutch the rpms stay where they were 2000 or even 3500. I have to pay attention more how I even end up in this state, usually I press the clutch in while coming to a stop so.... when in this state, stuck at 3500rpm, once I press in the clutch, the rpms drop to normal, or more often than not they drop and do the bouncy thing I explained above.

some aspects of these kinda makes me wonder if there is a transmission component that communicates (speed/gear/wheel-speed) with the computer and maybe that is what is wrong? keep in mind this is a manual :)

any suggestions?

i've changed the IAC valve twice and redid the PCV valve and hose... or do I have a vacuum leak somewhere, or air being pulled in post MAF?


thanks
 
My first guess is a vacuum leak. Check all the hard vacuum lines. I'll bet at least some are cracked. I replaced all mine with rubber vacuum line, the appropriate connectors and the stock fittings.
 
I too have a 1st gen manual tranny, and have had those same symptoms. Except my rpms dont seem to fluctuate nearly as much, usually bouncing between 650 and 1000. And just recently ive noticed it happens EVERY time i turn the wheel while at a stop. This leads me to believe that something with the power steering is causing this idle problem.. Ive had this issue for some time, coupled with the rpms not wanting to drop when in neutral unless i keep the clutch pressed in for some time. This is pretty annoying, because i have to adjust my driving to compensate for this delay in rpm droppage. This issue seems almost non-existent when i drive the car harder, keeping the rpms above 3500 for gear changes. This makes me wonder if its simply supposed to be driven harder, or if something is indeed wrong..
 
nastynaters said:
I too have a 1st gen manual tranny, and have had those same symptoms. Except my rpms dont seem to fluctuate nearly as much, usually bouncing between 650 and 1000. And just recently ive noticed it happens EVERY time i turn the wheel while at a stop. This leads me to believe that something with the power steering is causing this idle problem.. Ive had this issue for some time, coupled with the rpms not wanting to drop when in neutral unless i keep the clutch pressed in for some time. This is pretty annoying, because i have to adjust my driving to compensate for this delay in rpm droppage. This issue seems almost non-existent when i drive the car harder, keeping the rpms above 3500 for gear changes. This makes me wonder if its simply supposed to be driven harder, or if something is indeed wrong..
Click to expand...

If you're talking a hesitation for the RPM to drop to idle that's normal. It's an emissions thing......
 
your talking about right after startup, correct? i know the rpms are supposed to be higher at startup, and gradually lower to idle around 750 i believe? i know thats normal, but this happens long after the car is warm. the idle drops to around 600 or 650, then itll shoot back up to 950 or 1000, then drop back down etc.. only at idle though, and not all the time. and as i stated, i recently just noticed the rpms drop to that 600 range when at a stop and i turn the wheel.

im also experiencing the exact same symptom the OP stated, where i can put the car in neutral while moving, and the rpms wont drop (maybe VERY gradually), unless i hold the clutch in, sometimes taking a whole few seconds before the rpms drop to idle. its my understanding, atleast with other cars, that as soon as you put the car in neutral, it should drop down to idle. just seems very unresponsive in that regard, forcing me to keep the clutch pressed in in order to get the rpms to drop to idle.

Thanks, Nate.
 
Have you cleaned the throttle body? Might be getting hung up on gum. If you clean it, use throttle body cleaner, not carb cleaner, and keep the cleaner out of the electronics.
 
alright ill try that. any specifics i should know before doing this, or should it be pretty straightforward. ive only cleaned the TB and MAF sensor on one other previous car, but i still have the CRC brand stuff for both. And can i also clean that IAC valve with TB or what? I believe that valve is right next to the throttle body?
Thanks
 
I keep reading not to use any cleaners on the TB, as they will strip off the protective coating. Not sure where to go from here, besides just wiping it real good with a clean towel. Any suggestions?
 
thanks for the input everyone. i think this problem is broader than just at start up or just being a hesitation to drop to normal idle (if i dont press or release the clutch the rpms will stay high indefinitely)

the throttle body is clean so... LS4me, youre right I'll start by doing a thorough inspection of my vacuum lines.

nastynaters this part is interesting I'll experiment with it
This issue seems almost non-existent when i drive the car harder, keeping the rpms above 3500 for gear changes.
Click to expand...

also I think steering while stopped at idle will cause your rpm to drop low (even to 650) because of the strain on the engine to move the tires/rack while not rolling (dry steering)...
 
jokken said:
...also I think steering while stopped at idle will cause your rpm to drop low (even to 650) because of the strain on the engine to move the tires/rack while not rolling (dry steering)...
Click to expand...

There is a pressure switch on the steering system to let the PCM know about the extra demand. This allows it to maintain idle with very little change.
 
joegr said:
There is a pressure switch on the steering system to let the PCM know about the extra demand. This allows it to maintain idle with very little change.
Click to expand...

wow, i did not know this, could this part go bad? does it often?
 
jokken said:
wow, i did not know this, could this part go bad? does it often?
Click to expand...

Anything can fail. I don't know about how often. Usually, they are replaced because they are leaking.
If you have a scan tool that can initiate the KOER (Key On Engine Running) self test, the steering pressure switch is tested. (You have to turn the steering wheel a little at the right point in the test. The test fails if the switch doesn't react.)
 
joegr said:
Anything can fail. I don't know about how often. Usually, they are replaced because they are leaking.
If you have a scan tool that can initiate the KOER (Key On Engine Running) self test, the steering pressure switch is tested. (You have to turn the steering wheel a little at the right point in the test. The test fails if the switch doesn't react.)
Click to expand...

cool, thank you, my mechanic will let me use his scanner at his shop, I will check this out. thanks
 
nastynaters said:
I keep reading not to use any cleaners on the TB, as they will strip off the protective coating. Not sure where to go from here, besides just wiping it real good with a clean towel. Any suggestions?
Click to expand...

Mine was sticking closed, and I cleaned it out with a clean dry paper towel. Didn't take much. No problems now for over a year.
 
Alright thanks regiment1. And about the dopping idle hesitation, i do believe we have a very similar issue, though your may just be a bit more severe. The idle will not drop, or will VERY slowly, unless i keep the clutch in. And that steering pressure switch comment is interesting.. Im overdue for a atf flush n fill on there, so maybe thatll help a bit.
 
nastynaters said:
I keep reading not to use any cleaners on the TB, as they will strip off the protective coating. Not sure where to go from here, besides just wiping it real good with a clean towel. Any suggestions?
Click to expand...

They make a cleaner specifically for the TB, which I've never heard of causing a problem with any coatings on the TB. I wouldn't hesitate to use it on the TB for my LS, but if you aren't comfortable with it then you don't have to use it.
 
Yea im just gonna use it. Even says on the back of the CRC cleaner thats its safe for coated TBs
 
Recently did vcg's, plugs, coils, and imtv o-ring. Cleaned what I could, mainly the throttle body which was very gummed up, and looked over all visible vaccum lines. Now this hanging rpm issue is even worse than it was before. Curious if anythings been figured out with this yet. I'm starting to think maybe IAC valve, but it just seems like a vaccum leak.
 
Now that I think of it, I remember something with the vent hose that attaches from both valve covers (in a T) to the air intake. They both snapped into place firmly and seemed to seal, but the passenger side valve cover connection seemed to sit kinda funny and uneven. Could a weak seal there possibly cause this issue?
 
My car will be in the shop for about the next week cuz some kid decided to pull out right in front of me, so I'm hoping to have an idea of what to try when I get it back. Any advice is appreciated, thanks.
 
Sorry to hear that. Yes, any leak in the vacuum system will cause problems. But, if you wanted to be a sneak and haven't been talking about the car already, ask the shop why the car no longer idles when you get it back.
 
Lol yea I actually told them just after the accident I started leaking coolant. Which is happening, but is probly just coincidence. These little problems are keeping me from really enjoying the car. Hopefully they can atleast pinpoint the leak for me, as I haven't been able to.
Also not looking forward to removing the manifold again to replace the crankcase vent hose. It's cheap enough though so it's worth a shot. Seems ALMOST possible to sneak that passenger side connection on with the manifold intact. Maybe with the right screwdriver or something.
Any specific tips on cleaning the IAC? Never done that before. It's mounted on the side of the TB right?
 
On the plus side, doing the vcg's n whatnot seemed to solve my cold starting issue. 3 of 6 plugs were almost completely submerged in oil. Only about 1/2in of the top of the plug was visible
 
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