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Rough Idle - always

F

Force4

New CEG'er
Joined
Oct 1, 2007
Messages
8
For some reason my car can not hold a steady idle, it runs perfectly fine but as soon as it goes into nutrual it drops to about 300-600rpm and pretty much stalls out and then revs itself up and constantly does this no matter how warm the car is. It is not sluggish and runs perfectly fine. Also, when I come to a stop my peddle vibrates really bad, that would be a warped rotor correct?

Its a 1997 2.5l 5-speed.
 
No you feel a warped rotor only when you are moving, usually with the brakes applied.

Mike
 
I'm having the same idle quality problem. It seems to have happened about the same time the cold weather hit, although I've been having lots of P0171/P0174 check engine lights (lean condition). I took out my IAC valve (idle air control) and cleaned it last week, although it didn't look too dirty. I'm going to change it out for a new one in a few days (it's on order at Checker). I've been looking for vacuum leaks for months to fix the CEL's, but this is the first time my engine has not run well.
 
Spikedog, I have that same engine code error. Another odd thing is that it does it on and off now. It does it about 70-80% of the time its in neutral. Also, the pedal vibration is only when I am slowing down. :shrug:
 
The pedal vibration sounds like rotor warpage. Front disc brakes wearing out - mine went bad at about 38,000 miles on my '96 Mystique. Midas did me a good repair job, as they have lasted another 60K miles (so far).

As far as the 0171/0174 codes, I've replaced fuel pump, fuel filter, all 4 O2 sensors, PCV valve, cleaned the MAF 5 times, and sprayed carb cleaner all over the vacuum lines looking for a leak. If nothing else, I've acquired lots of new tools because of this (OBDII reader, vacuum gauges, O2 sensor socket, multimeter).
 
P0171 and P0174. Massive vacuum leak. Look for a broken vacuum hose.

Vibration when stopped could be broken engine/tranny mounts.

Per TSB, some of the causes of P0171 and P0174,

P0171 - System Too Lean (Bank 1) The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The code is set when the adaptive fuel tables reach a rich calibrated limit.

Fuel System:
· Contaminated fuel injectors
· Low fuel pressure or running out of fuel (fuel pump, filter, fuel supply line restrictions)
· Vapor recovery system (VMV)

Induction System:
· MAF contamination
· Air leaks between the MAF and throttle body
· Vacuum leaks
· PCV system concern
· Improperly seated engine oil dipstick

EGR System:
· Leaking gasket
· Stuck EGR valve
· Leaking diaphragm or EVR

Base Engine:
· Exhaust leaks before or near the HO2S
· Secondary air concern
Powertrain Control System:
· PCM concern

P0174 - System Too Lean (Bank 2) Same as DTC P0171, but Bank 2. See Possible Causes for DTC P0171
 
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I did a computer recalibration yesterday, and the rough idle is gone. Pulled #4 & 11 fuses, did the driving routine, and it runs fine now.

Of course, I did this on the drive to the parts store to pick up the IAC valve I had on order. The new IAC is still in the shopping bag. Plus, yesterday was the first day since the problem cropped up that was above freezing.
 
Spikedog said:
I did a computer recalibration yesterday, and the rough idle is gone. Pulled #4 & 11 fuses, did the driving routine, and it runs fine now.
.....
Click to expand...
If you did not fix anything, the the codes will come back.
 
Oh, the codes are still there alright. The engine runs great even with the perpetual 0171/0174 codes, gets 24-25 mpg, and accelerates just like it always has. When I replaced O2 sensors, the CEL was out for almost a month, and I got only 22 mpg. Quite frustrating, and getting expensive to chase the light for little to no performance improvement.

As I've hijacked this thread already, could the MAF be guilty of creating the lean codes? If its calibration is off or it just can't get the hang of running at 6000' elevation, couldn't that create the lean condition. It was changed by the dealer about 6 years ago, although I don't remember the exact CEL code (once again it was running fine, just didn't like staring at the light).
 
Spikedog said:
Oh, the codes are still there alright. The engine runs great even with the perpetual 0171/0174 codes, gets 24-25 mpg, and accelerates just like it always has. When I replaced O2 sensors, the CEL was out for almost a month, and I got only 22 mpg. Quite frustrating, and getting expensive to chase the light for little to no performance improvement.

As I've hijacked this thread already, could the MAF be guilty of creating the lean codes? If its calibration is off or it just can't get the hang of running at 6000' elevation, couldn't that create the lean condition. It was changed by the dealer about 6 years ago, although I don't remember the exact CEL code (once again it was running fine, just didn't like staring at the light).
Click to expand...

You might get lucky by cleaning the MAF sensor with some CRC electronic cleaner. When was the last time the PCV valve was changed?
 
Could be a bad DPFE sensor as well. That will generate a lean condition. You're issue will come back I almost gaurantee it.
 
todras said:
Could be a bad DPFE sensor as well. That will generate a lean condition. You're issue will come back I almost gaurantee it.
Click to expand...

You've also said you checked the vacuum bundle at the back of the motor. Have you replaced injector oring and nose seals? Also, Crankcase pcv valve and/or hose and/or gasket on oil separator cap that pcv hose connects to. Replacing the gasket on the oil separator cap is a little tough in between the cylinder heads but it can be done.........This is a rubber gasket ususally and can leak......

Bob
 
btrautman said:
You've also said you checked the vacuum bundle at the back of the motor. Have you replaced injector oring and nose seals? Also, Crankcase pcv valve and/or hose and/or gasket on oil separator cap that pcv hose connects to. Replacing the gasket on the oil separator cap is a little tough in between the cylinder heads but it can be done.........This is a rubber gasket ususally and can leak......

Bob
Click to expand...

Thanks for the suggestions, guys. I changed the PCV valve in September, same time as the O2 sensors. I haven't messed with the DPFE sensor yet, other than to take it off to get at something else. I cross-threaded one of the bolts on that bugger, and have a nylon spacer on the bolt to snug the DPFE sensor up to the aluminum intake.

As far as injector seals or intake manifold leaks, I'm not sure I want to tackle that without knowing for sure that's the problem. Too much $$ thrown at it already in vain.
 
Although I agree that a vacuum leak is the most likely problem, there is another obvious item to take care of.

At the risk of sounding like a broken record CLEAN THE THROTTLE BODY. This should automatically be included when servicing the IAC.

The physical symptoms could be explained from a dirty throttle body. The codes indicate something more. BUT CLEAN THE THING TO GET IT OUT OF THE WAY. It should be done occasionally as preventive maintenance.
 
BIg Jim - thanks for the suggestion. Previously I pulled one of the PCV hoses out of the rubber accordian hose and fired off several shots of carb cleaner while the engine was running. I've read some threads about more intensive cleaning, but it didn't look that bad that I needed to attack it with a toothbrush.

What would be the logic behind the throttle plate being dirty vs. lean condition? If the MAF is reading correctly, it should read airflow into the throttle body regardless of plate cleanliness. Is there some feedback loop with the throttle position sensor?
 
At least two things. The dirt in the throttle body keeps the throttle plate from fully closing, throwing off the throttle position sensor reading. The adaptive strategy adapts for the throttle position sensor reading change, but only up to a point. I have seen many times where the idle is weird because the adaptive strategy memory was dumped (as in changing the battery) and the throttle position sensor reading is so far off that it cannot adapt all at once.

The second reason for cleaning them both at the same time is if you leave the sludge nearby, the IAC may very well start acting up again very soon.

I'm not saying that I know this will solve your problem, but it should be done to get it out of the way and/or as preventive maintenance.
 
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