KirkF

I have a question:

Does anyone know if porsche changed anything in the programming of the DME eeproms between 89 and 91 to handle the difference between the early porsche single mass flywheel and the heavier dual mass flywheel? (regarding idle)

My car is a bit of an anomaly because it is an 89 c4 with a 91 C4 DMF transmission in it. Previously I had always blamed the poor idle on the LWF installed in the car, but now I find with the DMF it is not that much better. Idle still oscillates.

I know it is nothing to do with the intake because I changed all the parts during my engine rebuild from the earlier cast aluminum intake to the later style plastic ones including all the associated parts, except the AFM.

So now I am wondering if they changed something in the eeproms.

Any ideas?

Kirk

TR6

Just a thought... I was told by one mechanic that the ISV can eventually become worn to the point of needing replacement/rebuild. Symptoms would be an unstable idle. Have you checked the ISV internally to ensure it is moving freely with no binding?

KirkF

When I switched to the plastic intake, i switched out the ISV as well. (I got the plastic intakes with all their associated components except the air flow meter)

I cleaned the new ISV with parts cleaner, and it looked ok. (Cant say I actually tested it though).

But the idle problem is still there with two different ISVs.

Kirk

JasonAndreas

The maps are the same and the only code changes added support for the tiptronic.

If you remove the ISV and shake it you should hear/see the internal valve move freely.

Can you borrow an AFM from someone? Did you clean yours when you had everything apart? The ISV regulates the throttle bypass but the AFM is still used to monitor the actual amount of air that is entering the engine.

Geoffrey

Jason, I thought that at idle, there is an idle map based on the throttle position switch, not the afm voltage. Is that correct?

Red rooster

Kirk,
Maybe post your DME number , Porsche number and Bosch ?

Geoff

Lorenfb

"Jason, I thought that at idle, there is an idle map based on the throttle position switch, not the afm voltage. Is that correct?"

No, the AFM voltage does have control, but the idle map does an effect.

For this problem, all the basics need to be checked, e.g. fuel pressure, temp sensor.
The AFM is rarely a problem unless someone has "played" with it.

JasonAndreas

The TPS from the tiptronic input to the DME control unit is an off/on switch the same way the WOT and IDLE speed switch are used with the manual gearbox. I'm pretty sure the TPS was meant only for the tiptronic ECU?

The AFM is always used to calculate a base injection time even at WOT.

Have you ever seen one with a lazy or "sticky" response or does that just not happen?

Red rooster

Jason,
I have a Tip throttle pot/switch. You are quite right. The pot is used by the Tip
controller only.

Geoff

Lorenfb

"Have you ever seen one with a lazy or "sticky" response or does that just not happen?"

If it's lubed (WD40 on wiper inside & 30W on the flapper pivots) every 50-75K,
basically no problem.

KirkF

I'll have to go out and dig up the number on the DME, but its the stock DME from an 89 C4 with a stock chip. I think the number on the eeprom was 1267355759. (its hard to see in the picture I took)

Kirk

LeRoux Strydom

You could always get someone with a bosch hammer (or maybe the aftermarket unit discussed in the diagnostics threads) to perform an idle adaptation. Everytime your battery is disconnected, this dme setting is lost. This is applicable only to cars with O2 sensor.

KirkF

I've got a hammer and I've done the adaption. It didnt solve the problem unfortuneatly.

Kirk