ammonman

If I've been running hard for a while and have the car completely warmed/heat soaked sometimes the idle will drop so low that the car stalls. It will restart without any trouble, but then idle is very lumpy until I blip the throttle. The idle lifts back to normal after a good clearing of the throat but will stall again if it sits idling for very long. Thrust bearing is fine based on measurement with a dial indicator and a visual during MM/OPG replacement. I recently replaced the ISV in an effort to eliminate the problem. Fuel regulator and dampers are 3 or 4 yeas old. My last thought is my MAF or LH is on the way out. Any suggestions/ideas as to where to start looking? Car has plenty of power and runs great off idle. If the car is at temp but not heat soaked idle speed is fine and stable.

Mike

Ducman82

check the vacuum lines to the dampeners see if they have fuel in them.

NC928S4

I had similar problem. Temp Sensor II tested bad and was replaced. Problem solved.

ammonman

I'll check both of those items. I changed the Temp ll a couple of years ago and replaced the rubber boot. Maybe there is an issue with the wiring. I'll check the sensor from the LH connector and see what I find.

Thanks

Mike

Lizard928

I'm having a similar issue on an S4, the MAF sensor is testing to be bad and the signal varies greatly in different temperatures.
When cold the car will barely run because the MAF signal is 190-200 at idle.
When regular it sits around 110 which seems normal for the area, when heat soaked in traffic the car wants to stall as it's leaning out.

James Bailey

Could be the idle stabilizer valve is sticking when hot allowing the idle to be too low and stall....I have heard of this.

SeanR

I fought it on my car for years and the only way I've been able to get a good idle is using the Sharktuner cheat which takes the Bosch idle program out of the loop completely. It's only in a Beta test so far but it has my thumbs up.

For stock cars I have no idea what is causing it and have found no solution to the low idle problems some of us have. I hope there is something that I'm overlooking because there are a few customers cars who have this issue.

ammonman

The ISV is new as of last Wednesday. Other than the cold idle the MAF problem described matches my symptoms to a T. I'll check this as well. Thanks.

Mike

Mrmerlin

Mike I would consider swapping in a new temp 2 connector these wires can get pretty well cooked and then shed insulation
also get the MAF rebuilt
and consider checking the O2 sensor for correct output

ammonman

Thanks for the input Stan. I'll check the Temp ll wiring carefully. The O2 sensor is fairly new (in the last 2 years) so I don't think that is the problem. I'm leaning toward a failing MAF. I am going to borrow a spare MAF and see if the symptoms persist as they are very strongly dependent on temperature of the engine bay.

Mike

Mrmerlin

I have swapped out more than a few temp 2 sensor connectors.
and cut back the wires some to get to fresh conductor

ammonman

I had previously replaced the rubber boot on the Temp II plug so I peeled it back and checked the condition of the wires. There were two spots of missing insulation parallel to each other. As a temp fix I coated the spots with liquid tape and then a wrap of liner-less rubber electrical splicing tape. While I had everything apart I checked for continuity to ground through the harness (Temp II plug disconnected) and checked to see if the Temp II wires were shorted together anywhere inside the harness. everything checked out fine. I then checked resistance of the Temp II sensors from the LH and EZ-K plugs Both were where they should be for the current engine temperature. After I buttoned everything up I took a short drive and the idle dipped to 600 rpm when coming to a stop and seems to struggle to come back up to 650-700 rpm. I'm going to get a loaner MAF and see if that solves the issue. If so, I'll get a reconditioned unit.

More to come.

Mike

ammonman

Swapped in a loaner MAF today and replace the MAF connector and boot. There was one MAF wire with a crack in the insulation. While I had the old plug cut off I unplugged the LH and checked all the other wires to see if they were shorted to each other or to ground. All checked out fine. Installed the loaner MAF and fired it up. Idle settled in at 700rpm in Drive. The resistance of the idle circuit in the loaner was 411 ohms versus 384 in my old MAF. WSM spec is 1000 ohms or less so not sure if the 25 ohm difference matters. I'm going to run this loaner MAF for a few days and see if I get different results than my MAF. If so, I'll get a reconditioned unit.

Thanks for all the input.

Mike

John Speake

The idle pot is not used for your S4, assuming it is running with O2 sensor.....

If the problem re-ocurrs, check the throttle closed switch is switching correctly when the engine is hot.
An over tight throttle cable or faaulty switch can cause it to hang open circuit, so the idle stabiliser isn't triggered. The TPS can suffer from fractured solder joints.

ammonman

Thanks John. The TPS is new as of last week ('94 and up GTS switch and kickdown relay for Dynamic Kick-down ). I'll check the idle portion of the circuit when hot if I continue to have issues.

Mike