Idling issues

[ldstang50]

My gf (has a 97 rs)just had her motor rebuilt cause of a bad piston ring. new everything. gets the car back, 1day later she has lidling issues. it idled at 1600rpm in park and neutral then in drive it idled at 900rpm. when she would stop while in drive it would stall, but if she put it in N it wouldn't stall. then she had electrical issues. We replaced the alternator and got a new battery (solved elec issue) and installed an idle speed controller. The car now idles at 1300rpm in P and N and 800 in D or R. It still stalls out if she stops while in D but if she puts it in N it wont' stall. The vacuum lines LOOKED to be all sealed. I'm thinking maybe an electrical line in the shifter or something with the tranny is messed up and thats why it idles high. There is something the tranny is sending to the computer to adjust the enigne rpm for. There is no check engine light. Any ideas? Doug or anyone?

 

[xxthayxx]

have u double check the timing? if its off by a tooth or two it could cause rough idleing aswell.

 

[Doug99RS]

I called her today and said to check the throttle cable. If it's too tight then it will hold the throttle plate open at "idle". However, this doesn't account for the stalling out issue.

I'm still really interested to hear that you guys checked for intake leaks a second time using carb cleaner or wd-40 or something. I know the crew checked but I'd like to hear that you did as well. I'm specifically interested in possible vacuum leaks at the injector o-rings, EGR Tube, EGR Valve, and other vacuum lines.

The transmission really I think is a long shot here. It sounds more like a vacuum leak or possibly timing. Only thing with the timing is that if it was off, it would be driving like it did before the rebuild. But it doesn't. When it drives fine... it drives better than before right?
Doug

 

[dave99gst]

a/t tranny gets all its shift patterns from the TPS signal be sure thats set correctly.
i dont see BISS mentioned anywere ?

vacume leak could cause hi idle.

 

[EclpzLvr97]

I called her today and said to check the throttle cable. If it's too tight then it will hold the throttle plate open at "idle". However, this doesn't account for the stalling out issue.

Doug this is Liam under Nikki's name. Throttle cable is not taught like you say. Thats one thing I knew to check sorry to not say that.

I'm still really interested to hear that you guys checked for intake leaks a second time using carb cleaner or wd-40 or something. I know the crew checked but I'd like to hear that you did as well. I'm specifically interested in possible vacuum leaks at the injector o-rings, EGR Tube, EGR Valve, and other vacuum lines.

I was at class tonight and haven't had a chance to take another look at it. Where should I be looking for vacum lines now? I will check the EGR valve tomorrow and hose on the EGR valve. I didnt' think to check the o-rings on the injectors I will do that tomorrow.

The transmission really I think is a long shot here. It sounds more like a vacuum leak or possibly timing. Only thing with the timing is that if it was off, it would be driving like it did before the rebuild. But it doesn't. When it drives fine... it drives better than before right?
Doug

I am at her place now, she said the when you start the car when its cold it idles fine both in P and D. But when it warms up is when it has its issues. Now it idles normal (about) in D. In P it idles 1500-2000rpm. Other than that it drives fine, and changes gears fine. Acceleration and power are fine also.

 

[EclpzLvr97]

a/t tranny gets all its shift patterns from the TPS signal be sure thats set correctly.
i dont see BISS mentioned anywere ?

vacume leak could cause hi idle.

Dave love your car man, I love those rims on the black!
TPS sensor, how would I check to see if its set correctly?
Also why would it idle normal in D but too high in P?
BISS? Basic Idle Set Screw? Not quite sure what you mean by BISS, sorry

 

[EclpzLvr97]

Doug, I know you said not to really mess w/the idle screw....but when *would* you take that as an option?? Just curious to know more about that.

As for the stalling....it would stall when I would come to a complete stop.....about the time when the a/t transmission makes that funny zipper-type noise. However, since replacing the idle speed control motor, it hasn't stalled yet....not sure if the replacement is why or not. It still will kinda jump sometimes, but it hasn't stalled yet. Just seems weird how it acts most normal while it's still cold but once it warms up is when it acts up.

So yes, it's a bit better than before....but part of that I believe was b/c of the bad alternator maybe. There was a point right before the alternator went bad that my gears were going crazy....I had absolutely no acceleration and/or power. That's all void now though.

 

[Doug99RS]

The zipper type noise is the transmission solenoid pack on the front of the transmission. It's a bunch of valves opening and closing changing the paths that the transmission fluid takes through the valve body. I still don't think the transmission has anything to do with it. The timing of the problem just happens to occur when the transmission makes a gear change.

I'm glad you mentioned that the problem is not there when the engine is cold. That rules out an uncontrolled vacuum leak. Vacuum leaks don't just come and go. This still does not rule out the EGR valve because it is a moving part that WILL change states at different points in the drive cycle.

Dave, I have been really anal about not telling them to mess with the BISS because I was afraid it would mask their actual problem. The BISS on the 2gnt's is harder to get to and does not unscrew itself easily like 4g63's do. Plus since Liam now posted that it idles fine when cold that tells me Base Idle is fine.

Liam, Do you know if Keith replaced the thermostat?

Can you find a scan tool and check the throttle position sensor signal? It should be about 0-3/4% and not more.

Also check the wiring for the TPS and IAC motor. The normal path is routed under the intake. I have seen a couple cars come in where the wiring was laying on the EGR tube causing the protective wire loom to start melting to the tube.

I'll see if I can't get some more help in here as well.
Doug

 

[92awddsm]

No, I didnt replace the thermostat. That was on the list of maintanence items after I gave the car back to her. The loom is also ran under the intake like it was factory. When I pulled the engine apart, I never messed with the tps. I left it attached to the tb and just set it aside. I did seperate the intake and remove the injectors for cleaning. When we checked for vac leaks, I used wd40. Nothing turned up. The timing is definately set properly, and nothing is any different than before. Could the overcharging alternator have caused any other electical issues resulting in a high idle?

 

[Doug99RS]

When it comes to the computer... alot of things are possible. If the idle air control motor is new, the wiring is in tact and the idle concern only shows up after the engine warms up then that leads me to believe it may be either thermostat related or computer. Thermostat being cheaper, I'd start there.

Without the car in front of me I'm hesitant to suggest the computer too given the expense.
Doug

 

[ldstang50]

CEL is on. code 31. Here is what it means. What am I to exactly check and possible replace? She says she's had the code before the rebuild of the motor. So now what?
31
EVAP solenoid circuit
Evaporative purge solenoid / Clogged purge line / Vacuum hose / Evaporative emission canister clogged

 

[Doug99RS]

Could be the vacuum leak we've been looking for. On my RS the evaporative purge solenoid is located under the passenger side headlight. If you have the tear drop shaped covers out, you can reach right up in there and grab it. There's two vacuum lines going to it. If you remove the coolant resevior and move it to the side you can see where the vacuum lines come up through the frame. One goes to the back of the car and the other goes to the rubber hose that leads to the throttle body vacuum fitting. Check those lines for vacuum leaks. Under the coolant resevior you will also see a line that has a green cap on it. This is a test port for the evaporative emissions system. This is one of the suspect lines.
Doug

 

[EclpzLvr97]

Just a little update, for you especially, Doug....

A few days ago now, I noticed my car idling correctly again when I put it back into Park. When I noticed this, I tried it out in Neutral and then in Reverse....I was happy to see the idling was not jumping and staying up like it used to do when I put it in these gears. I didn't wanna get my hopes up so figured it was a fluke and would faithfully screw up the next morning.......well, the next day on the way to work, still normal and has stayed that way ever since.

So, I am not sure how the car just suddenly decided to idle properly. The only thing I can think of is that I started driving the car how I usually did before the rebuild. When I first got it back from Keith, I was easy on it.... then after the "break in" period, I drove it my way..... as in, sometimes to slow down the momentum of the car, I hit the over-drive button to raise the rpm a bit rather than tap the brakes. Not sure if this triggered something in the ECU or what, but after driving it like that again, it started working great.

So, Nikki and her Dizzum are happy together once more. Thanks for everyone's help. It's great to have a properly working DSM.
(Please don't break now that I said this.)

 

[Doug99RS]

These computers do have adaptive memory and can learn a driver's habits to a small extent. Don't know if that was the case here or not but I'm glad it's back to normal now. Thanks for the update,
Doug