95carrera

Trying to upload video for my first time.

In drive idles okay but when in park or neutral, no bueno.

Speedtoys

When was the last time, if ever, a top-end refresh was done?

ICV comes to mind.

95carrera

That's when it started. Last week, New plugs, fuels lines, vacuum lines, rebuilt injectors, new fuel regulator, various other little bits, new CPS.

jcorenman

Other than the surging idle is runs OK? If so that rules out most things.

A surging idle is often a too-lean condition. That can be an air leak (vac or breather hose disconnected or connected incorrectly), worn MAF, maybe incorrect injectors. The ISV can also be an issue, but the usual failure is that they stick, causing either a high or low idle-- but not surging.

Video shows 120K miles, has the MAF ever been replaced with a rebuilt? MAFs get progressively leaner with age (i.e. they under-read air flow, causing less fuel to be injected). The LH compensates (with the O2 sensor as a reference) up to a limit. Useful lifetime for a MAF is 80-100K miles, depending on start-stop cycles (the burn-off when the engine is stopped is the source of most of the wear).

What about the O2-sensor? Has that ever been replaced? As they age they also cause a lean mixture, and by 60-80K miles are about done. The LH cannot compensate for this, because the O2-sensor is the reference sensor. The replacement is a Bosch 13048 Oxygen Sensor, around $70 from Amazon or your friendly parts purveyor.

95carrera

Car ran fine before I started "improving" it

Started with Porken Chip install and 87' fuel regulator. Ran fine after that. Once shortly after it failed to start on first crank.

Couple weeks go buy, I do the fuel hoses, vacuum lines, new CPS, new plugs and bought a set of the Bosch Ford part # injectors, confirmed they fit, had right part number etc. Hot starting immediately started, Cold starts fine.

After a couple of weeks idle problem started, now getting worse even in drive while stopped at light thought it might die on me.

Car is making vacuum for first time in awhile because all the lines were disconnected when I got in there.

MAF has not been tested. Need a loaner as it is my daily driver and Kevin from Injection labs misplaced his loaner last time we talked.

I might try the oxygen sensor. Is that one on the exhaust above the cats on top?

jcorenman

Check with Louie Ott, he handles JDS Porsche (John Speake) rebuilds on an exchange basis. Website here, click on "Contact": https://www.performance928.com/

Yes. You'll need to remove the six bolts connecting the exhaust to the exhaust manifolds, so that you can drop the front of the exhaust a few inches for access. Watch the cable, it snakes from the O2 sensor over the heatshield and then through the side of the tunnel to a disconnect in the CE-panel area-- rubber 3-pin connector.

worf928

What year is this 928? We can't actually help you if we don't know what it is and if earlier than '87 we needed to know if it's ROW or N.A and transaxle type (that, regardless of year.)

95carrera

Thanks, 85' us model auto.

worf928

Good. Now, put that info in your signature and from here on out you won't need to think about it anymore.

Ok... so... What could you have disturbed during all of this work that could cause your problem?

Or is it more likely that something would have just failed due to your mere presence?

Both can happen, but the latter is less likely.

What's most likely is that there are a few things still not-quite-right and something else was disturbed during your work.

An auto dying in Drive at a stop is a classic sign of the Mass-Air Sensor being out-of-spec.

However, in Park or in Neutral, not.

Your gauges indicate that the engine is warm.

Does the erratic idle happen upon a cold start? Or does it idle more-or-less smoothly for a minute after a cold start?

Or is the erratic idle most pronounced when the engine is nice and warm?

Stop. Diagnose first. Then throw parts.

Here's my guess...

On the S3s (pre-S4 32vs) there's a ~8" pigtail harness from the WOT/Idle switch to the main harness. It has 3 pin connectors made of the same material as the CPS connector and 87'+ knock sensor and Hall sensor connectors. These connectors crumble to dust after 15+ years.

When that happens, the idle switch circuit can be compromised and thus, when the engine is warm the LH 2.2 ECU will not know that it is supposed to engage the idle stabilization control loop. The result - with a working 02 sensor - will be erratic idle as the as the 02 control loop sweeps through its control range once the engine is past its cold start-up period.

You need to test that the idle switch closed signal is being received by the LH. There is a way to do this with a multi-meter. If you have the WSM on CD-ROM there is an LH/EZF troubleshooting procedure that will give you step-by-step instructions.

If you are not up to that, and just want to make a 'good guess' and throw a part at the problem, then order a replacement pigtail harness. The OE harness is NLA (last time I checked), but, I think Roger has after-market replacements.

The OE pigtail harness _always_ goes bad. So, even if that doesn't completely fix the problem, then you've spent money on good preventative maintenance no matter what.

If, indeed, the idle switch signal is causing the erratic idle, you may find that the engine still wants to die at a stop when in D due to an old mass-air-sensor.

HTH

EDIT: I failed to tie everything together: It is possible - even highly likely - that you disturbed the pigtail harness when you were doing all the work after your Porken chip install.

95carrera

Does the erratic idle happen upon a cold start? Or does it idle more-or-less smoothly for a minute after a cold start?

Or is the erratic idle most pronounced when the engine is warm?

EDIT: I failed to tie everything together: It is possible - even highly likely - that you disturbed the pigtail harness when you were doing all the work after your Porken chip install.[/QUOTE]

​​​​​Cold starts are fine. Warm starts are difficult like fuel starved. Idles worse when warmed up.

worf928

If I was a betting man:

- pigtail harness to idle/wot switch is causing the warm erratic idle (or, just a bad idle swtich part of the WOT/idle switch, but that's rare)

- hard warm starts and dying in 'D' at a stop are an out-of-spec Mass-air Sensor.

You can test/diagnose the former. You'll have to let go of your MAS for a couple of days for Kevin to test/rebuild, or find a 'spare' to send to him.

95carrera

Exactly where is that one located? Photo appreciated. Thanks

Speedtoys

Its the wires going to-from the throttle...you know where the throttle is on the intake?

PorKen

Start with a known baseline. A S3 at 120K+ with original parts? Replace everything. Refresh the intake hoses as necessary.

Rebuilt MAF, new O2 sensor, TPS, ICV, CPS...everything that was recommended before installing S300s chips.

Check that idle and WOT are getting to the ECUs. Set the idle and CO after jumping B->C.


The contrary view might be to replace as needed and do many checks, first. It will be very frustrating and you may learn a lot, but in the end you will most likely end up replacing everything. (AMHIK )

worf928

I have very few pictures of the S3 motors - and don't have one on-hand now for a fresh picture. I will look later tonight and see if I have one. On the other hand, there are plenty of S3 folks - some on this thread already - that should be able to dig up a good picture pretty quickly or via search as this pigtail harness has been covered.

Searching for pigtail harness or S3 idle/WOT switch may find a better picture than I can come up with.