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Car Still Down, Please Help

6K views 58 replies 8 participants last post by  Draike13 
#1 ·
So to recap on a long story/series of events that have lead me to here; here is a brief:

Car had issue starting. Took in and eventually had starter rebuilt. Working great now.
After starter replacement, battery wouldnt charge. Had alternator looked at. everything was fine. Went to replace fusible link. When i pulled that i noticed what the problem was with the charging. I had the line(Fusible link) from the starter to alternator on the jump post, not the 12v post of the starter solenoid. Fix, and car is charging and starting perfectly.

Since to first got the starter back in the car, a second problem arose. Car is now idling at just below 3000rpm.
*I did remove the air intake, TB, and Manifold to get to the starter. All is back properly(can really only hook up one way), no holes or tears in lines, everything looks and reads great.

On inspection, car is just having an issue with idle. when in gear and driving, it is perfectly fine. It just idles insanely high.
Tried relearning process. Nope
Tried 2 other possible ways i read about a relearn...Still Nope
Tried manually blocking some of the throttle body to limit air flow...car spins down and can get it to normal idle...or it dies because its difficult to hold that exact amount of closure.
**Suspicion? Throttle body is open to far at idle. Read somewhere where this can happen and it should be open at 6% on idle, and its stuck at 20% and idling at 3k. Confirmed...this is at least what it seems to be doing.

Next strange occurrence to this. If driving the car down the road, clutch out, and kick it out of gear, car will climb RPM till it hits between 4500-5500. then it will drop down to 1100-1200...then climb again and repeat.
If clutch is in, car will just idle at 3000. This is while going down the road. Many speed variations tested. Same across the board.

Last thing. After sitting for a day, the car will start and idle normally. 1100 or so. Then after driving it a minute, it will rise until it is idling at 3000 again.

Next. I replaced the TB. On the hope that the memory for it was located there and a new one would relearn. This did NOTHING. Everything is exactly the same.

Im at my end. Nothing is working. Any help, suggestions, trouble shooting would be more than appreciated. Im dying to get back on the road.

***Side note. Car did throw the P507 code, RPM idle too high. Which was sort of expected. It cleared and hasnt come back. But obviously is still idling too high.
 
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#2 ·
The PCV valve/connector could be leaking if it cracked, and you seem to have taken a lot of parts off that could leak - a boost leak test could be in order. Curious what it would do if the MAF was disconnected.

If you feel like those are probably all fine, or want to try something simpler; write down and clear any DTC codes (P507, etc) - assuming you have a scan tool or app on phone with bluetooth OBD2 reader. I believe the ECU will not relearn idle if there are DTC's present, so you may need to keep clearing codes while doing the next step:

"Now onto the best solution IMO. The best way I have found to bring the idle back down, is to force it. If you have a manual car, put the transmission in first with the e-brake up and slip the clutch until the idle is around the normal level. Do this multiple times and the idle will eventually stay there. Sometimes it will stay until you hit the throttle then it will jump back up again, don't worry mine did this too, just keep trying and eventually it will stay. It will take some time, mine took 3 days but now the idle is normal and the car runs great. If you have an automatic, my suggestion is to put the vehicle in drive with the a/c on. This might bring the idle low enough but chances are, a reflash may be your only solution."

More details and options (ECU reflash, driving the hell out of the car, etc)

- https://www.cobaltss.net/forums/pro...ng-throttle-body-fix-solution-answers-286328/
- https://www.cobaltss.net/forums/2-4...igh-idle-after-cleaning-throttle-body-322529/
 
#3 ·
Check for vacuum leaks or a faulty PCV.

It would be very useful to check the vehicle parameters to see what the ECM thinks the desired and actual throttle positions are.

I'm not saying it won't work, but I don't like the idea of slipping the clutch that much.
 
#4 ·
Wow guys thanks!
Already great ideas. I honestly have a hard time believing its a leak...though im not going to swear it isnt.
A crack could be the issue. I had it apart twice with the exactly same result as far as idle, so i have to imagine i didnt do it wrong twice(as for a faulty connection leak).

As for a leak elsewhere...possible, but wouldnt that make it harder to get the throttle to spin down when covered? because it would be getting air elsewhere? or am i thinking about it wrong?
There just doesnt seem to be a(apparent) leak.

I will definitely check the PCV first thing tomorrow, as well as fine tooth comb for cracks...
Barring that, looks like manual reset it is.
I didnt know this would do anything, thanks.

Will also be checking back for any further ideas.
 
#5 ·
After typing out the last response something did cross my mind...
I do have the DDMworks CAI.
Just for further investigation. Am i mistaken, or would that probably rule out the PCV issue? Hose it new(ish) and not connected to plastic.
Or am i looking at the wrong thing?
 
#6 ·
No the PCV could still be bad regardless of the CAI.

How modded is your car? Do you still have Your stock parts? A good place to start is put your car back stock and see if that clears it up.

Also have you checked your MAF? It usually would throw a code if faulty but it’s worth checking. Check wiring and Could Pull it to make sure it’s not broken, don’t touch the little diodes inside if you pull it out and check it. Those are what measure air flow and temps etc
 
#7 ·
Only under the hood mod is the CAI. Everything else is stock. And this is the 2.4 not the redline.

Location of the PCV? and yes, theoretically i could reinstall the stock air intake and see what it does... but ive had the CAI installed for probably 7 months with no issues from second 1 of install.
Would that make a difference?
 
#8 ·
New development.
I i tried to "Force to idle lower". It worked. after leaving gear or clutch back in car held idle wonderfully(though it was rough the entire time).
When i take off, seemed like when i was giving it gas, it would return to high idle.
So i let the car roll to a start after forcing low idle. Took off good, no gas, but then started to automatically open throttle. High RPM returned. Car was giving itself gas?(What?)

Im at a loss again. Not sure what else to look at.
 
#9 ·
I think you need a diagnostic scanner to see what the throttle is being told to do. It is the first step in the diagnostic instructions.

When you had the throttle body and manifold off did you clean the seal surfaces? There are warnings about not using MEK or sharp objects to avoid damage.
 
#10 ·
On the 2.4 there are only a few places you can have an issue.

If take off your air filter and, while the car is running, cover the end of the air intake where the filter normally would be, what happens?

Generally a high idle like you describe is caused by a leak somewhere after the MAF or a sticking throttle body.

The 2.4 only has 2 vac lines. One running from the intake manifold to the brake booster and the breather line from the valve cover to the intake is the other. Both, IIRC, are after the MAF and a leak in either could cause a problem.
 
#12 ·
This same (high idle) problem was discussed on the Solstice forum, and one of the guys found the actual throttle body relearn procedure in his service manual:

Start and idle the engine in park (or I presume, neutral) for 3 minutes.
Monitor the desired and actual RPMs with a scan tool.
RPM should begin to decrease.
Ignition off for 60 seconds.
Start and idle the engine in park (or I presume, neutral) for 3 minutes.
After 3 minutes the engine idle should be normal.
If the engine idle speed has not been learned, drive the vehicle above 44 MPH with several decelerations and extended idles.
If the engine idle speed still has not been learned, turn the ignition off for 60 seconds and repeat the process from the beginning.

IMPORTANT: If the check engine light comes on during the cycle with idle speed DTCs, clear the codes to allow the ECM to continue to learn.

So it appears that the ECM learns the correct idle speed on its own, but cannot do it if an idle-related DTC is set.
 
#13 ·
Ive tried this a few times now with the car not "Showing" a code.
I got a Fixd Bluetooth scanner and repeatedly cleared the P507 code that didn't seem to want to clear, even though it wasn't showing up on the dash.

I ran the "relearn" again, and now its idling at 3500rpm...even worse now.
Havent taken it out to drive since the even higher idle, but why would it go up?

Also, a few days ago I took it to the dealer and had the PCM reflashed. Did absolutely nothing.
 
#16 ·
Removing the filter and covering, or removing the entire CAI and covering the TB does the exact thing. Can limit the air flow until car dies down to idle lower.

This is with both the old and new TB, both did the same.
On checking car numbers from the OBDII reader, TB is open to about 25% at idle. On reading, shouldn't it be about 6%

When I force the lower idle(e-brake, and letting out clutch till it stays low on its own) it will set around 5-6%

Could a leak at the manifold be happening when covering TB is killing car?

My brother keeps saying he thinks it might have something to do with the MAF. Anyone else think so?

And as a note, only codes it has thrown this whole time is P507(High Idle...well duh) and P1400(cold start code? at least from what ive found)
 
#17 · (Edited)
My 2.4 idles with the throttle at 25%. If I load the engine with the clutch the throttle opening goes up to maintain idle speed, but mine is idling normally, so that second item may be moot.
Reading a lower throttle opening when loading the engine doesn't make any sense to me. Did you do anything with wiring? It almost appears to be reading backwards.

If you expose the throttle body, where is the throttle plate? Have you done anything to move it or block its movement?

What does your MAF read? I am seeing 0.6 lb/min at idle.

You probably caused the P1400 by dragging the engine speed down. I would not recommend that you do that any more. It has no practical value and is only destroying the clutch.

What temperature is your O2 sensor indicating for catalyst temperature?
 
#20 ·
Ok guys the old school way of checking for a leak is to spray Starter fluid and listen correct ?
I haven’t worked on a car in 10yrs so forgive me if I’m wrong
 
#28 ·
Ok, so here are screenshots of the actual numbers. Also let me explain how these are coming up.

When i start the car it is idling at the 2300ish rpm.
After forcing a lower idle(e-brake on, clutch slowly let out while in first gear till car lowers idle to about 800. Then clutch back in, car stays are 900ish, in neutral, clutch out) idling around 900

I have no idea still what is going on. My next step just because...well, its affordable, is to replace the intake gasket, hope to stop an air leak? Then im left with buy new already programmed ECU.

If anyone has any ideas to help that would be amazing. Really dont want to drop the money on another part that isnt needed if this is something stupid im overlooking.

PS, outside air temp today when running the car was 45F Text Font Line
Text Font Line Screenshot
 
#29 ·
Your throttle at 22.75% open is flowing more than twice as much air as mine is at 24% open.
Your throttle is flowing very nearly the same amount of air as mine is at normal idle (0.58 lb/min = 4.38 g/sec).

I think that you do not have an external air leak because the mass flow is reasonably equivalent to mine at normal idle, and you are indicating more air at higher RPM.
I think that you do have either a throttle butterfly/seat problem, an internal leak, a feedback wiring problem, or an ECM problem because your throttle at 16% is flowing as much as mine at 24%.
 
#30 ·
The TB is new. When this happened i replaced it with a brand new one.
0 change after doing that.
ECM problem is what i keep going back to. Ive read about the same sort of thing being caused by that. Which is why i had it flashed, which did nothing. Of course, i dont know exactly what they did...i have no decent place around here to take it to to have that done.

Could you elaborate on "feedback wiring problem" and "internal leak"?
If possible i would love to check on those things before going further.

Also, to the best of your knowledge. If it is a problem with the ecu(say its fried) and i buy a preprogramed ECU for this year of the car(I think the company i found said i would have to send them my vin to program it correctly) would that "Fix" the problem?

Like, no additional flashing or programming, that should handle it.
 
#31 ·
An internal leak would be something that lets air bypass the throttle, but still routes it through the MAF sensor, since yours seems to be reading appropriately for the engine speed. It would not include a gasket or PCV hose, for example, because any air entering those would not go through the MAF sensor.

Feedback is the normal term for signals that return to a controller to let it know what is happening with a device like the throttle body. There should be some sort of sensor on or in the throttle body that measures the butterfly opening, and wiring that sends that signal to the ECM. I have not looked at the throttle body wiring, so I do not know exactly how it is controlled or how the ECM knows how open it is. I will look at it tonight though, if someone hasn't posted information about it before then.

It seems unlikely to me that a "fried" ECM would work correctly except for one function. Controllers generally do not work, or fail, that way.

An ECM has to be flashed with your VIN to work in the car. That has to be done by someone with access to GM's network, but can be a dealer or independent mechanic.
 
#32 ·
Ok, great information.
I took it to the local dealer to be flashed. So Its sounding to me like somewhere along there, there has to be a leak.
Which i took the whole thing apart, twice. its very possible. I just cant seem to find it.

TB is new
ECU has been flashed by the dealer
Relearn has been tried MANY times(In all ways that ive read about, unless im doing it wrong)
Tried finding air leak, but nothing on the CAI.

If i understood correctly, a hose past the TB, or possibly...intake manifold?
 
#33 ·
I looked at a spare throttle body, then pulled the intake off of the one on the car, and I do not see any way for air to get into the engine except going through the butterfly if it is going through the MAF sensor. Your airflow reading tell me that all of the air is going through the MAF sensor.so that pretty much means that your butterfly is more open than it should be, and the question is why.

Did you check your throttle pedal position while this is happening? One option is that the throttle body is doing exactly what it is supposed to be doing based on a bad throttle position sensor..

Where is your throttle plate with the ignition on but the engine not running (obviously) and what does the position read?

This is mine at 26%.

Metal Brass


If I push the accelerator pedal to the floor it opens to just about straight open, and indicates 88%.
 
#34 ·
I looked at a spare throttle body, then pulled the intake off of the one on the car, and I do not see any way for air to get into the engine except going through the butterfly if it is going through the MAF sensor. Your airflow reading tell me that all of the air is going through the MAF sensor.so that pretty much means that your butterfly is more open than it should be, and the question is why.

Did you check your throttle pedal position while this is happening? One option is that the throttle body is doing exactly what it is supposed to be doing based on a bad throttle position sensor..

Where is your throttle plate with the ignition on but the engine not running (obviously) and what does the position read?

This is mine at 26%.

View attachment 111965

If I push the accelerator pedal to the floor it opens to just about straight open, and indicates 88%.
How have i not thought of this at all. wow.
I will find out when i get home and let you know.
 
#36 ·
I am not looking at a service manual, so i am not certain about the exact names or alphabetizations used.

There is a sensor (two actually) integral to the throttle body that reads the position of the throttle butterfly to provide feedback to the ECM.

There is also a sensor on the throttle pedal that reads its position to provide an input to the ECM to tell it how fast you want to go.

Both (or all three) readings are available in the ECM data that you should be able to read through the OBD port.

Have you looked at the actual position of the throttle butterfly to see how it compares to mine, and what the indicated position is?
 
#37 ·
I looked before and to memory, it looks like mine is in just about the same place.
And ok. Ill see if i can grab some more numbers from the OBD scanner later and report back. Im looking for pedal position basically? ill see what options i have and what i can find.
 
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