low idle on 3.2
 

Help needed to troubleshoot this low idle problem.

Here's the story...

I drove about 20 miles from work to home with no problems. The last 1/4 mile I thought I heard a low toned misfire then the car idling was rough like it was running on 5 cyclinders. I drove it into the garage and shut off the engine. I read some posts and added some techron the next day and started her up. Dead battery. I jumped the battery. Car started and I let her idle for about a minute. Idled around 900 rpm with no signs of rough idle. Then started to drop to 500 rpm engine was rough. I thought it was going to die so I shut her down.

I looked at previous post on low idles and what various members did. I know the basics about the engine but would classify myself as a newbie to a P-car engine. As you can see by the list it is very extensive. The battery is brand new and I don't know why it would be dead or if it related to this idle problem at all.

Where to start first? Any "most likely" culprit locations

Thanks in advance for any help.

Here's the list I have so far:

1. bad plugs
2. Idle control valve (ICV)
3. Crimped breather hose next to oil tank
4. Breather hose from oil tank to air filter
5. distributor cap/wires
6. fuel filter
7. alternator
8. cracked rubber line @copper vacuum pipe behind throttle body
9. battery
10. 4 prong connector (unknown usage) with DME type connector
11. voltage regulator
12. Warm up Regulator (WUR)
13. adjust valves
14. injectors
15. intake maniford gaskets
16. 02 sensor
17. CHT sensor (??)
18. spark plug wires
19. Rubber gasket on oil cap not sealing
20. DME (not relay)

I would start with the things that can be checked easily and cheaply (or free). ICV is easy (do a search-all you need is a paperclip). It can be cleaned easily and cheaply. Unplug the O2 sensor to see if that changes anything. If it regularly happens only after warmup that will tell you a lot. YOu listed wires twice (5 & 18) do you suspect a problem? Do a search on some ideas there.

well,first of all you can`t diagnose anything until you diagnose the dead battery.First things first amigo,with a wholly electronic engine management system the battery and charging system has to be fully operational before you can get ANY useful info.New battery? who replaced it? Why was it replaced? Check the battery terminals for tightness before you waste your time and use a mutimeter to see if the alternator is charging.Any other tests are useless without having done these things first.

My 88 car had a problem of cutting out and not wanting to restart when warm,when it was ticking over revs used to drop as if the engine was going to cut out then shoot up to 2500 rpm then back down to 900 rpm and so on.
Problem was dry joints on dme relay pcb (powers the fuel pump)
under lefthand seat-just move seat back as far ass possible-small black box with one nut holding it down-remove the connector from rear (takes a good pull/wiggle) pry off plastic cap to expose relays/pcb and look for cracks in solder (when relay gets hot problem appears)
repair or replace

What raceman said. You have to start with the basics. I would troubleshoot the battery problem first. If you have a dying battery or bad altenator/voltage regulator it would produce the symptoms you describe. I would also change out the DME relay because it is relatively cheap to do so and is good preventative maintenance. Clean all the battery and ground connections including the one on the tranny mount and see if this cures your problems.

test - disregard, sorry

when it's hot and at idle, disconnect an injector plug, or pull off a sparkplug connector one at a time, and see if you can locate a dead cylinder. a common problem on carreras is an intake gasket that got sucked into the port, causing an air leak and a dead cylinder at idle, as well as a low rpm stumble/miss. an exhaust gas test would show high hydrocarbons if this was the case.

thanks guys for the replies.

Raceman...In my haste I said the optima battery was new, its about a month old. Its been fine up until this episode. Sorry for the mislead.

I measured the voltage at the battery....5V. I rejumped her. She started OK an idled at about 1100 for about 15 seconds. I quickly measured the voltage across the battery and it read 8V. The idle then dropped very low I could not increase the idle via the accelerator. I had to shut her down.

What next? Seems like the alternator or the voltage regulator is bad since I do not get the normal 13.5V. How can I tell which one is bad or both are bad. Car has 122K miles.

KurtV, I did change the DME relay about 1.5 years ago. I ASSUMED the ground wires have good contact to the chassis, but I will check.

Keep the info coming. Your inputs are much appreciated.

Changing the voltage regulator isn't hard to do; it's not that expensive compared to an alternator. Had you notice your headlights dimming and then brightens in relationship with RPM prior to this? I changed mine recently for over charging.

This sounds like an alternator problem.

Jeff

IMO if you need an alternator, you will want to change the regulator as well. Start with the regulator and then do the alternator if the voltage
problem still exists.

I've read some posts with pelicanites having surging of their tachs and lights. I do not have the tach surging problem. I haven't been driving at night lately so I cannot say if the lights dim or gets brighter with the RPM.

I'll go ahead and replace the voltage regulator from our host as Joe recommends above followed by a new or rebuilt alternator as necessary

Hopefully this will fix the dead battery issue, then onto the rough idle/misfire if the car still exhibits those symptoms.

I'll post the results after I acquire and install the voltage regulator

So Falcon...
What did the problem turn out to be? On three occasions now I've had my 3.2 die or threaten to die on me when the idle drops low after start-up on a warm engine, or shortly afterwards between shifts. I'm able to bring the idle up to speed with the accelerator, but can't imagine what the problem may be... would like to know if in your case it was the voltage regulator or alternator going bad. Thanks.
Jlex.

jlex, I had a delay in finding some time to disassemble the alternator. No problem using Wil Ferch's writeup in the archives. After removing the VR from the alternator, I noticed that the there are two metal contacts from the VR that ride along the shaft of the alternator. The top contact (is this a brush?) was very short. Approx half the length of the lower contact. I suspect that the top contact was not riding on the shaft since the upper groove of the shaft was black with some material that most likely impeded the conductivity between the shaft and the upper contact.

I compared the new VR from our host with the worn VR and noticed that the contacts are about twice as long. Not sure if the PO ever replaced the VR. I decided to just recondition the alternator at the same time.

I found a local place that will recondition the old alternator for $85 if I supply the VR. They'll check the diodes and stator and clean everything up. I prefer this since I know that the housing will fit back into my car. The bad news is that the guy who reconditions the unit was out on vacation. I just turned in the alternator this morning and will get it back tomorrow.

I recharged my optima already and as soon as I get the alternator and VR back into the car. I'm ready to start up the car. I think this will definitely fix my dead battery issue. Possibly this may fix the low idle problem since the car will have a constant 12V+ for the coil after it started.

A buddy lent me one of those LCD voltage readers that fits into the cig lighter socket. I may get one for myself....they're less than 10 bucks via mailorder.

I have some pics of the blackened alternaltor shaft ring that I will post and will also post my results once I fire up the car.

http://forums.pelicanparts.com/uploa...1089763135.jpg

This shot shows the alternator grooves that the voltage regulator springed contacts ride on. Notice the top groove is black in color and the lower groove shows metal. I think the upper VR contact no longer contacts the upper groove as shown by the next shot.

http://forums.pelicanparts.com/uploa...1089763281.jpg

Here the VR contact are of different lengths. The upper being about half the length as the lower. Not positive if the upper is making any contact with the upper groove in the alternator. Either way I had the alternator shop machine the upper groove to remove the surface. I had the shop replace the VR (looked stock) with a valeo from our host and will install the alternator tonight or tomorrow.

The shop installed new bearings, checked the diodes, turned the grooves, blasted the fan/pulley and housing and tested the unit for $90.

I'll post the results after I install and crank her up.

Falcon: THanks for keeping us posted. The pix are really helpful. I'm just wondering if my couple of episodes with the low idle are alternator related & should serve as an early warning of problems to come.
I have around 50,000 miles only on my '85 carrera, so I'm not sure the alternator or VR would be acting up yet. Let us know how many miles are on your car... wasn't going to suspect mine until it was reaching about 100,000.
Can you believe they wouldn't have a dash gauge for the alt? What was Porsche thinking? A couple of years ago I did buy one of those digital meters that stay plugged into the cigarette lighter... seems to work pretty well. My readings have been within normal specs so I'm leaning away from an alt. problem unless someone out there says there can be intermittent problems. Thanks again for keeping us posted.
jlex.

The pics were a great help ( thanks for the plug on my R&R article , BTW..)
It is clear that the "slip rings" are worn on one of these...that's why it's black..its the base bakelite or plastic that is underneath the copper. you have no electical contact there. The other slip ring is deeply grooved and in trouble. The two srpring loaded "prongs" on the VR are not metal...they're carbon brushes.
You need to have the alternator rebuilt ( new slip rings..I'd also go with new bearings, have the diodes checked) and add a new VR....should get you there.
---Wil

jlex, The odometer reads 122K. I would suggest measuring the voltage across your battery before, during and while your car is at low idle. It should read about 13.5 Volts. If you are getting that voltage during the low idle then your alternator and VR is properly supplying voltage to your system. I would look elsewhere downstream for the electrical such as wires, distributor, plugs. There could also be fuel problems such as an intermittent fuel filter problems. Check my list I initially place on the first post of this thread. Possibly start your own thread based on what you already checked. I'm sure someone will chime in too help.

Wil, thanks for the lesson on the alternator. Since my alternator passed the electrical test done by the shop. I would assume that they replaced the slip rings. The diodes where checked and I saw new bearings installed.

I got the alternator housing onto the altenator and was just about to place it back into the car last night but I lost the sunlight. I should finish up the install tonight.

John - My car (from time to time) suffers these exact symptoms. My wrnech also mentioned the sucked in intake gasket - However, he sprayed some stuff over the intake manifolds and said it was unlikely that the gasket had been sucked in after his test. Does that sound right?

If you use MAPP gas or such and (carefully) spray it near the intake gaskets...and if the engine speed changes....you found another un-metered air path that would indicate a loose ( or sucked-in) gasket. If the engine speed didn't change...you're OK...for now
--Wil