a little help here - Carrera bouncing idle

[JeremyD]

Ok - not a good P-car weekend. Went to drive the Carrera and the idle is all loopy. I noticed it on Friday - This has been a reaccuring issue - seems to go away and resurface.

Last time - about a month ago - I was having the idle problem and an intermittent cut off - complete loss of power then fine again. Almost enough of a problem that I considering not doing a DE.

Well this time it started when the gas tank started getting low - was running fine right before that.

Now I filled up and can;t shake the idle bouncing all over the place - the car eventually dying.

Last time I replaced the fuel filter - and the distributer cap and rotor - and switched out the DME relay. Then I cleaned all the grounds - and ran a full day at a DE.

I've also cleaned thoroughly - my Idle control valve - including unplugging to assist with my troubleshooting to no avail.

I've spent the last two nights reading fixes all the the way from plugs to fuel injectors to rebuilt DME - Any recommendations on where to go from here?

[Dueller]

What kinda chip you have in it?

[ghnat]

Check fuel pressure to see if any particles are blocking fuel delivery.

Cyl head temp sensor? - when was this last replaced?
How old are the speed and ref sensors?
How old are the spark plug wires?
That's all I can think of right off hand.

[don911]

This is a long shot but I've had similar idle issues and it was the connector that goes into the AFM. Have you removed the connector to the AFM recently? When I changed AFM to MAF, two of the contacts pushed back out of the connector and caused bad A/F mixtures.

If you pull the boot off the connector, you can check and make sure the contacts are all the way in. Long shot but it only takes a few minutes to check.

[JeremyD]

Originally posted by Dueller
What kinda chip you have in it?

Steve wong custom chipped mapped to my engine. The car has run like a champ for the last 3500 miles.

Originally posted by ghnat
Check fuel pressure to see if any particles are blocking fuel delivery.
Cyl head temp sensor? - when was this last replaced? 3500 miles ago when the enine was redone
How old are the speed and ref sensors? 3500 miles ago when the enine was redone
How old are the spark plug wires? Original - 62000 miles
That's all I can think of right off hand.

I'll check the AFM - but no work was done in the area lately

[Dueller]

I had anothe rbrand chip that did this but SW's cleared it up.

I dunno...bad tank of gas? Long shot but the letting the tank get low caught my eye...water will settle to the botom. But not likely it if you were sloshing it around.

Keep us posted

[JeremyD]

it was doing it before the fill up

[JeremyD]

So - the short version - What's been done so far:

CHT - replaced at engine rebuild 3500 miles ago
Both Reference Sensors - replaced at engine rebuild 3500 miles ago
Chip - custom programmed by Steve Wong for 993 SS cams - car has been running like a champ with a pretty solid (but lumpy idle for the past year)
ICV - Thoroughly cleaned Sunday
Disributer cap - replaced last month
Rotor - replaced at engine rebuild 3500 miles ago
DME - Replaced a month ago
Grounds cleaned - battery/transmission/motor and Fuel Filter replaced last month

So after some reading in the archives - seems like the possible candidates for this typr of problem range from a faulty DME box - to plug wires.

So, before I start sinking some money into this chasing an unknown - Where to start?

Spark plug wires? They are original (but only have 62,000 miles on them)
Fuel injectors? I can send off for recondition and flow testing
DME? Trade for a reconditioned one?

Any other suggestions?

[wcc]

O2 Sensor? Disconnect it and if it runs and runs smooth then maybe it's time for it to be replaced. I'm just guessing JeremyD, but that's easy and free to disconnect just to rule it out.

[JeremyD]

Thanks - No O2 - has been disconnected since my rebuild - Steve programmed the car to run without from the beginning.

[Zeke]

Originally posted by JeremyD



Fuel injectors? I can send off for recondition and flow testing

That's a distinct possibility from my reading here. Won't cost you much to find out.

[wcc]

If you think it may be the plug wires, couldn't you find the resistance (and Continuity) and just measure the ones you have. That shouldn't cost anything unless you don't already have a meter.

Here's a cheap one if you need it:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90899

Have you tried replacing the Fuel pump relay? Can you hear the fuel pump come on before you start the car? I thought they can be intermittent. Just for a test you can use the AC or the horn relay cause it's the same.

[JeremyD]

Really the spark plug wires "look good" I went over them with a fine toothed comb - no cracks in the insulation - I do have the multimeter - just not too much of clue on how to use it.

For ~ $100 - I can get the fuel injectors cleaned and flow tested pretty easily - at least take that off the table.

[450knotOffice]

Wow! I can't believe no one has brought up the distinct possibility that the mixture and idle speed setting are mis-adjusted.

Jeremy, about 1 1/2 years ago my Carrera was doing the EXACT same thing...and I mean EXACTLY. The engine's idle would get very "bouncy" and would cycle from about 600 RPM (and almost die) to about 2,000 RPM. It would lope like this for maybe up to a minute before usually settling down. On a couple of occasions I would be slowing for a corner, come off the gas, press in the clutch, and the engine would just shut off. Embarrassing, to say the least. Also, at a steady state cruise I could feel just the slightest surging. It was annoying.

I looked at all of the usual suspects without luck. I cleaned the ICV which changed nothing and then replaced it. Still no change. I checked the O2 sensor. It was OK. I checked everything. Finally, I gave up. I took it to my mechanic, they hooked it up to a gas analyzer and found that the idle mixture and idle speed, which are apparently co-dependent, were way off. They adjusted it perfectly, tightened up a few straps which secure the 90 degree rubber elbow to the AFM and throttle body and...

It ran perfect! It has run absolutely flawlessly since that day. It turned out to simply be the base idle mixture and idle speed settings that were significantly off their marks which was causing the whole mess. Interestingly, the idle speed shown on my tach had seemed to be within the normal range so it never entered mind that it and the mixture were way off. My mechanics said that many of these cars have the same mixture/idle speed problem and a good adjustment with a gas analyzer usually cures the problem.

Try it.

By the way, for you CIS guys, this does not apply to your cars. This is a Motronic issue.

[madmmac]

Have you tried swapping your DME relay again?

I changed mine just because I wanted a spare and the car idled better and was more responsive when first starting out in 1st gear...much less drop off.

For about $30 bucks or if you have a spare already, just give it a shot.

[JeremyD]

Thanks Scott - I saw the thread where you had this issue - but there was no resolution.

[JeremyD]

Originally posted by madmmac
Have you tried swapping your DME relay again?

I changed mine just because I wanted a spare and the car idled better and was more responsive when first starting out in 1st gear...much less drop off.

For about $30 bucks or if you have a spare already, just give it a shot.

And yes, I swapped it out again - no change.

Scott - did yours run fine all the other time? As in - when you got on the gas - no issues, right? Mine only seems to do it when I come up on a light or start out.

[450knotOffice]

Hmm. Yea, I guess I need to update that thread. I'll do it right now.

[450knotOffice]

Jeremy, the car ran great when I was on the gas. It had problems at idle and very low throttle settings - like during steady state cruise (when I'd feel the very slight surge, almost imperceptible).

[JeremyD]

and this is probably magnified by my 993 ss cams. Steve W warned me that I have to have a perfectly functioning ICV and mixture and idle speed settings. Thanks for your help.