Why would my car surge and stall like this?
03-15-2013, 01:03 PM
#1
Why would my car surge and stall like this? My car has been like this ever since the build last summer. Trying to to get out of my uphill driveway it will surge and most of the time stall.
In reverse its a total nightmare. Any time I give the car throttle in reverse it is just about guaranteed to surge then stall.
Usually it is very rare for the car to act up on the street coming to a stop but today just sitting in traffic I noticed there was a slight non stop surge of maybe 100rpm or so.
I took a vid of what happens when the car is just at idle, in park, and I rev the engine. Watch the 2nd time I rev, the rpms just surge up and down almost stalling untill it finds a steady idle. Then, watch the 6th time I rev, it does the same thing but this time stalls.
In reverse its a total nightmare. Any time I give the car throttle in reverse it is just about guaranteed to surge then stall.
Usually it is very rare for the car to act up on the street coming to a stop but today just sitting in traffic I noticed there was a slight non stop surge of maybe 100rpm or so.
I took a vid of what happens when the car is just at idle, in park, and I rev the engine. Watch the 2nd time I rev, the rpms just surge up and down almost stalling untill it finds a steady idle. Then, watch the 6th time I rev, it does the same thing but this time stalls.
Last edited by senicalj4579; 03-16-2013 at 11:53 PM.
03-15-2013, 07:11 PM
#3
My hc a4 car never surges while driver, revving, or in park; however, after I shut if off, if I fire it up real quick it idles rich on my wideband, 12.1 or so for 15 second and it surges for a good 5 seconds. As long as I don't touch it, it bumps back up.
Def not an answer, but it could be rich after it sees throttle then searches for idle. Idk why my car does it. My car is also in the 12's for the first 45 seconds it's on. Rest of the time solid 14.8 to 15.2 and 12.5-12.7 solid at wot.
Def not an answer, but it could be rich after it sees throttle then searches for idle. Idk why my car does it. My car is also in the 12's for the first 45 seconds it's on. Rest of the time solid 14.8 to 15.2 and 12.5-12.7 solid at wot.
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03-16-2013, 11:26 AM
#11
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If it isn't throwing any codes, maybe it's the IAC, TPS, or a vacuum leak. Try to start with those. If I remember correctly, I had a vacuum leak and IAC valve issues (two different cars) and with both of them the car would try to find the idle. But, it would also run pretty crappy at times too with a vacuum leak.
Good luck
Good luck
03-17-2013, 12:48 AM
#13
The IAC is the only thing that can do that to your engine. Now the question is.....Is the IAC itself going bad? Or is something else wigging out and telling the PCM wrong information making it tell the IAC to wig out.
Buy a new IAC and try it. If it doesn't fix it, return it for a refund after cleaning it up real good.
Then I would grab the wire bundle that's coming immediately out of the PCM and move it side to side and forward and back while the engine is idling.....see if it surges. If it does, your PCM-to-engine ground wire could be loose.
Something is telling the PCM to operate the IAC.....or the IAC is going bad.
And NO......you will NOT get an SES light or code until it totally fails.
.
Buy a new IAC and try it. If it doesn't fix it, return it for a refund after cleaning it up real good.
Then I would grab the wire bundle that's coming immediately out of the PCM and move it side to side and forward and back while the engine is idling.....see if it surges. If it does, your PCM-to-engine ground wire could be loose.
Something is telling the PCM to operate the IAC.....or the IAC is going bad.
And NO......you will NOT get an SES light or code until it totally fails.
.
03-17-2013, 12:51 AM
#14
The IAC is the only thing that can do that to your engine. Now the question is.....Is the IAC itself going bad? Or is something else wigging out and telling the PCM wrong information making it tell the IAC to wig out.
Buy a new IAC and try it. If it doesn't fix it, return it for a refund after cleaning it up real good.
Then I would grab the wire bundle that's coming immediately out of the PCM and move it side to side and forward and back while the engine is idling.....see if it surges. If it does, your PCM-to-engine ground wire could be loose.
Something is telling the PCM to operate the IAC.....or the IAC is going bad.
And NO......you will NOT get an SES light or code until it totally fails.
.
Buy a new IAC and try it. If it doesn't fix it, return it for a refund after cleaning it up real good.
Then I would grab the wire bundle that's coming immediately out of the PCM and move it side to side and forward and back while the engine is idling.....see if it surges. If it does, your PCM-to-engine ground wire could be loose.
Something is telling the PCM to operate the IAC.....or the IAC is going bad.
And NO......you will NOT get an SES light or code until it totally fails.
.
Thank you very much man I will try that and report back
03-17-2013, 07:32 AM
#15
Joe I completely forgot that when I first got my car it'll sometimes surge (bone stock) in the rain or randomly after I would get on it and would be stopped at a light and after I swapped my IAC and TPS it fixed it 100%. Try that before doing anything else.
03-17-2013, 10:55 AM
#17
There's like 4 things.....TPS, MAF, MISFIRES and I think failing 02 sensors......that can all send messed up signals to the PCM causing surging.
I think that's the 4 things. A failing coolant Temp Sensor on the 1998 models like mine can also cause ALL kinds of crazy **** to happen and the engine will run horribly. My car won't even run with a bad or unplugged Coolant Temp Sensor, it surges, backfires, coughs and then stalls. I think the later years don't have that problem.
.
03-17-2013, 11:53 AM
#18
True. The TPS can also send bad signals to tell the PCM, which will then make the IAC open and close causing the surging.
There's like 4 things.....TPS, MAF, MISFIRES and I think failing 02 sensors......that can all send messed up signals to the PCM causing surging.
I think that's the 4 things. A failing coolant Temp Sensor on the 1998 models like mine can also cause ALL kinds of crazy **** to happen and the engine will run horribly. My car won't even run with a bad or unplugged Coolant Temp Sensor, it surges, backfires, coughs and then stalls. I think the later years don't have that problem.
.
There's like 4 things.....TPS, MAF, MISFIRES and I think failing 02 sensors......that can all send messed up signals to the PCM causing surging.
I think that's the 4 things. A failing coolant Temp Sensor on the 1998 models like mine can also cause ALL kinds of crazy **** to happen and the engine will run horribly. My car won't even run with a bad or unplugged Coolant Temp Sensor, it surges, backfires, coughs and then stalls. I think the later years don't have that problem.
.
I know that you cant tell if they are bad by looking at them but I did take out the tps and iac. They look pretty damn clean. I re installed them and let the car run in driveway. Tried messing with wires,wiggling pcv hoses,wiggling hoses to intake, and no change in idle.
I dont have time to buy new iac and tps today. I still debating to do that or not. I guess I should.
But heres a question...can a messed up vss cause the iac to do wierd things too? The funny thing is the problem im having with the surging/stalling is MOSTLY when im pulling out of my uphill driveway or when im in reverse backing up anywhere.
And another question...if it did have anything to do with a vss issue would the car absolutely have to be rolling? Because if the car has to be rolling in order for the vss to mess with the iac then I could rule the vss out seeing how I get the surging/stalling while in park (just like the vid shows)
03-17-2013, 11:59 AM
#19
Ok guys, after I re installed the iac and tps back in I got a p0122 tps code. I assumed that the code maybe just because I re installed it. Should the tps show a code after re installing it? Its weird though. It showed up on my obd scanner but no engine light.
03-17-2013, 01:16 PM
#20
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Have you looked at TPS voltage values since seeing the pending DTC/plugging the sensor back in? You should never see a value below 0.2v (idle) or above 4.7v (WOT) with the key ON....if you do, there is a problem. Idle is usually around 0.6v.
This may have just been a result of you plugging/unplugging the TPS while there was power in the harness. I'm not sure I'd worry about it, unless the values are off or the pending code matures and trips the MIL. I would, however, double check that the connector is in good condition, clean, and fully seated.
As for the surging, that is an unacceptable amount IMO.
- What are your IAC vaules (as reported by scanner) during the surging, and also when the idle is stable?
- What do the TPS values look like during the surge, and also when the idle is stable?
- What do the LTFTs look like?
- Does your throttle body have a small hole in the throttle plate like a stock one would?
Since this started with the H/C swap and not randomly at some later point, I believe the issue will be traced to some part that was replaced or damaged during that process, or something in the tune itself. I know we talked a bit about this last year. You said that the tuner has looked over the situation and can't find anything wrong....so has he offered any suggestions of alternate possibilities based on his experience?