Low idle in Drive/reverse

[AWDtalontsi96]

Got me a low idle problem in my gfs 97 eagle tsi fwd auto

First off Im far from a newbie. I been working on DSM's since 95' but this is my first automatic.

She got the car for 500 bucks in pieces. Spent a month putting it all back together. ripped out the s afc , put the stock 450cc back in it. resolidered all wiring , heat strinked everything. All emissions solenoids and hoses , egr valve. no boost leaks.

current mods and parts replaced: injen intake w/open air elment , true greddy type s bov , upper ic , lower ic and j pipe on a MHI big16g , cated downpipe , thermal cat back , walbro 255 , hallam boost control. fp dsm manifold. New wires , new plugs , had a bad mass air sensor , replaced with used working one i had around my shop , new timing belt , water pump , front cover , timing pulleys , balance shaft belt , new rear o2 sensor , new belts.

Only check engine light is fuel pressure solenoid and I am pretty sure that isnt causing the low idle in drive and reverse.

Also stock ecu.

I base idle set screw right around 750-819 rpms. This is what evo scan is telling me.
TPS is right around 12-13% and at wot is 100% So I knew thats working.

I have a feeling the iac is working as well cause on cold starts it holds the idle at 1100-1200 rpms and lowers as car warms up.

My problem is when car goes into any drive gear the idle drops to 600 rpms. Never stalls , doesnt run like crap. Just idles at 600 rpms.

So are we talking about bad ecu grounds cause the car did sit around for maybe 6 months to a year in pieces. or is it a bad drive/reverse switch thats not telling the ecu to bump the idle.

Like I said i got almost 20 years working on DSMs and evo's but this is my first automatic so I am stumped.

 

[007jimmy]

My rpms drop as soon as load is applied also. I have my idle set on link @1000rpm. With load its at 750-850ish. Try raising idle in park. Just make sure you ground timing and adjust slowly. Your TPS should be 0, why is it at 12%??

 

[ed1380]

It still might be the iac. While idling in park move the steering wheel back and forth. Does the idle raise? If not, its the iac. High idle when cold is not an indicator of the iac working. High idle is done by the wax thermostat in the throttle body.


The ecu has a desired idle for p/n and for d/r. Check the wire that tells the ecu what the shifter position is.

 

[ed1380]

My rpms drop as soon as load is applied also. I have my idle set on link @1000rpm. With load its at 750-850ish. Try raising idle in park. Just make sure you ground timing and adjust slowly. Your TPS should be 0, why is it at 12%??

The tps will never be perfectly 0-100%
Mine ranges 7-96%

 

[007jimmy]

My TPS% on link is zero. The volts are .63.. No experience with evoscan, sorry.

 

[AWDtalontsi96]

My rpms drop as soon as load is applied also. I have my idle set on link @1000rpm. With load its at 750-850ish. Try raising idle in park. Just make sure you ground timing and adjust slowly. Your TPS should be 0, why is it at 12%??

Yeah TPS can be off some when in the closed position 11 to 13%. But wot should always be 100% from what I heard and seen in link or in evo scan if the ecu doesnt see 100% it wont go into closed loop mode or open loop.

It still might be the iac. While idling in park move the steering wheel back and forth. Does the idle raise? If not, its the iac. High idle when cold is not an indicator of the iac working. High idle is done by the wax thermostat in the throttle body.


The ecu has a desired idle for p/n and for d/r. Check the wire that tells the ecu what the shifter position is.

Where the is sensor on the tranny for the park/netural switch. I know which wire goes in the ecu for the signal.

It still might be the iac. While idling in park move the steering wheel back and forth. Does the idle raise? If not, its the iac. High idle when cold is not an indicator of the iac working. High idle is done by the wax thermostat in the throttle body.


The ecu has a desired idle for p/n and for d/r. Check the wire that tells the ecu what the shifter position is.

Will do the steering wheel test tomorrow. good idea. I got a spare iac at the shop i can swap in too.

 

[ed1380]

IIRC it's 80% to enter open loop

the sensor is on the trans. under the fuse box. big 20 something pin plug. right next to the shifter cable.

 

[AWDtalontsi96]

Okay so I had it warmed up and idling in park at 750 and turned the wheel real quick back and fourth. Idle didnt change at all really . Didnt jump up and really didnt drop either. Then put it in drive. Idle dropped to 600 rpms like it has been , jerked the wheel back and fourth quick and idle stayed about the same. Kinda dropped some , but def never increased. So I guess it sounds like the iac