[No.15]

So I am trying to figure out an issue with my new to me 968.  When cold the engine stumbles.  Rev it up and it will almost stall when you let off the gas.

 

I am attaching a video, sorry i\I left the door open and it is beeping.  I already replaced the o2 sensor thinking it might help.  Once the car has been driven awhile it seems to recover.

 

https://youtu.be/BN3spZ5AdF0

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[MCL968]

Use the search function (the little gear looking thingie next to the search bar) and look for ICV or Idle Control Valve. I believe ICV problems have been linked to symptoms such as yours.

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[ds968]

ICV  ( sometimes also referred to as ICS - idle control sensor ) is indeed the most probable culprit.  However, there are a million and one other things which could cause that cold start stumble issue, with everything running perfectly fine after the car is warmed up for five minutes or so..   

 

small vacuum leak

coolant temp sensor 

02 sensor ( but you already replaced that ) 

distributor / rotor/ etc

ignition coil

spark plug wires

fuel check valve

injectors

 

and if its a tiptronic , add the secondary ( tip ) computer to the possible list 

 

I don't meant to scare you, but start with the cheapest troubleshooting component and work your way from there .   ICV won't be the cheapest..    

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[pdxmike]

ICV would also be my guess. There is a DIY on this site on how to R&R.

 

However Dan is correct that there could be a dozen or more causes. I would check the DME temp sensor first. It's super easy to get to (blue connector front and center) and inexpensive if it's the culprit.

 

Next after the DME temp sensor I would suggest checking fuel pressure at the rail. It's hard to get the right fitting but for a quick check you can use a cheapo FP or oil pressure gauge and use a hose clamp (super tight!!) on the threaded port and it will work fine. Also pull the vacuum lines off the FP regulator to make sure you don't have a leak - any fuel coming out of the vacuum lines is evidence the diaphragm is shot. You could have a problem anywhere along the line impacting fuel delivery cold. Fuel pump, check valve, fuel filter, injectors, regulator - any of them could be faulty. The car needs less enrichment warm so that idle drop would get better.

 

Do you know when plugs/wires/rotor/cap were last replaced? If you don't know - like the O2 sensor - it's probably time.

 

(As an aside - while I doubt it is the O2 sensor - the newer Bosch universal replacement MUST be installed with the included posilock connectors. It cannot be soldered or crimped with regular connectors. Believe it or not, the sensor gets reference oxygen through the wire strands. It doesn't make a lot of sense to me either but the info is straight from Bosch. I originally soldered my O2 sensor and saw significant improvement in the O2 sensor response time on the Durametric when I switched it to the posilock kit.)

 

Did you get the belts done? Sounds like they are whining to me - might just be the recording - but that's the sign that the belts are too tight. Might - maybe - be putting extra load on the engine cold....

 

Finally - easy fix - you can pull the door chime relay if it gets annoying. It's right above the hatch release switch. It's the relay with a perforated circle for the speaker.

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[pdxmike]

I listened to your vid a few more times - I think one or both of your belts are way too tight - I would definitely get that addressed before going too far down the rabbit hole with the rest of your diagnostics.

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[No.15]

Thanks everyone

 

Belts were just done 200 miles ago (should I bring it back for adj?)  and cap and rotor were checked at that time and deemed good by mechanic.  Spark plugs were changed as well.

 

I will give it a once over and do the things suggested here.  Could be vacuum leak for sure, car has been driven less than 2000 miles in the last 10 years, it has 120K total. 

 

It sat unused for a long time so I had all the belts, fluids and normal maint items done before I started driving it.

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[pdxmike]

Glad to hear you had the belts and tune up done.

 

There's variable opinions about the belt whining. If your belts are brand new they might whine for a while then improve. Some cars just seem to be more whiny than others.

 

I will say that my car whined like crazy when I first got it - belts were 4.5 years old - and after the belt replacement they were close to dead quiet. Just did the 2000 mile retension and my belts are very quiet compared with your vid. (Wish I could say the same about my lifters...)

 

If you didn't have the idle drop issue I would say just leave the belts alone - but given that you're having this problem and you've got that whine going on - I would rule out overtensioned belts creating too much load on a cold engine at idle. JMO.

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[No.15]

I made 2 more vids.   about 20 minutes after a long drive

 

Idle

https://youtu.be/SvSsXwZ8E78

 

revving

https://youtu.be/wq_xTxglT2M

 

Thanks again for everyone's help

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[J.Elenbaas]

The whining of the belt is probably caused by the idler pulley (944 102 277 06) which should be adjusted with a 0.5mm gap clearance to the balanceshaft belt running below and a preload of the upper part with 0mm to 1mm.

 

Regards,

Jack.

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[Ryan]

Did you do a blink test to see if any code errors appeared?

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[No.15]

I did the blink test and I get a 1-5, All clear

 

I ordered the arnnworx belt tensioner.  I figured I better learn how to do this right considering I have the 968 and the 951.  I'll probably end up with another 944 type car knowing how I behave.

 

Anyway, I see this car is going to devil me.  I went out this morning to see if I could find any vacuum leaks or anything obvious and wouldn't you know its not doing it today. 

 

I think part of the problem is this car sat for so long that everything is just needing to get their legs back so to speak.  When it first came off the transport truck you could tell the lifters were not pumped up and it took a few minutes for them to come alive.  Hopefully the transport driver was easy on the car (arggh) when this happened the belts were over 20 years old and 40k miles.  Car sat from 2010 to 2019 gaining less than 2000 miles but its in surprisingly good shape

 

I am going to clean the MAF and the throttle body and see what that gets me.  I am going to order some vacuum tube before I start messing around in case something disintegrates when I move it.  I guess I should do fuel lines as well but they seem ok on quick inspection.  I think they were done in the past because I know the car got a fuel pump and regulator at one point.

 

I have an ac issue I am going to start a different thread on.

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[pdxmike]

If you are confident enough to use the Arnworx, I would highly recommend getting a Durametric. It will make diagnosing problems like this SO much easier as you can see all the sensor data in real time.

 

You will need an older Windows laptop or Mac with windows capabilities to use it.

 

It is really an amazing tool considering the vintage of these vehicles. I was able to see my O2 sensor's fluctutations improve in realtime after correcting the solder job on the wiring. It will tell you everything - RPMs, throttle plate angle, O2 voltage, timing advance, coolant temp, etc. You'll be able to diagnose and rule out sensor issues - at the DME no less - without even popping the hood.

 

And - you can clear the airbag light!

 

Durametric has refurb units. Give em a call.

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[94SilverCab]

Now that the belts have been done, may I suggest that you take the car on a very long drive (like 100 miles) without shutting the car down. Push every button, headlights up and down, turn the steering wheel from end to end. Sometimes it just take a good number of heat cycles and use to shake out the bugs.

 

At worst, you get a few hours of driving   

 

Jay

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[No.15]

If you are confident enough to use the Arnworx, I would highly recommend getting a Durametric. It will make diagnosing problems like this SO much easier as you can see all the sensor data in real time.

 

You will need an older Windows laptop or Mac with windows capabilities to use it.

 

It is really an amazing tool considering the vintage of these vehicles. I was able to see my O2 sensor's fluctutations improve in realtime after correcting the solder job on the wiring. It will tell you everything - RPMs, throttle plate angle, O2 voltage, timing advance, coolant temp, etc. You'll be able to diagnose and rule out sensor issues - at the DME no less - without even popping the hood.

 

And - you can clear the airbag light!

 

Durametric has refurb units. Give em a call.

 

Thanks for the heads up.  They did have refurb units available so I ordered one.  Seems like it's a tool similar to forscan which I use on my Ford vehicles, except forscan is free

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[pdxmike]

Awesome. 

 

The port is in the passenger side footwell, right above where the pass R foot would be. Should be a big round cap over it. Very strange pre-OBD connector. 

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[No.15]

I think as SilverCab posted this thing needed a few heat cycles.  I have driven the car on some long distance runs and it behaves slightly different every time I take it out.

 

I have used either Gumout all in one or Redline cleaner in the last 3 tanks of fuel.  I cleaned the MAF and throttle body and adjusted throttle cable, in addition to other items listed.  Electrical connector on the MAF was corroded  so I used a small file and cleaned the contacts. 

 

Went from car stalling a lot and running real rough to a somewhat smooth idle.  Still not as smooth as I would like but I am going in the right direction.

 

Realizing as I work on this that everything I touch in the engine bay has a risk of disintegrating in my hands .  I'm exaggerating but I have crumbled some rubber bit's it the last few days.

 

Don't know what is normal MPG wise for these but I started tracking on my second fill (4 now) and I have gone from 18.1 to 21.8 hand calculated in the last couple of tanks.  I have not been driving it to easy either.

 

Now I need to get my volt gauge to work (it's pegged) and my fuel gauge to be more accurate. 

 

Again thanks everyone.  Hopefully as I progress I can go from asking to answering questions.

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[unknown4u]

Have you already changed the dme relay?

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[MCL968]

Fuel gauge accuracy is always a crap-shoot. Mine improved when I pulled the cluster to do the bulbs and the light tunnels and the odo gear, and I cleaned the posts where the gauge connects to the PC board. Do that for all of the gauges and the accuracy will improve.

 

Given how long the car sat, I would send the injectors off to get cleaned and calibrated. My 92 runs so much better after that little intervention, and the cost was surprisingly low.

 

These are the folks I used: https://www.rcfuelinjection.com/

 

And the idle on these cars is not like modern cars either. I have never seen one that didn't wander a bit. I attribute that to the old style idle control valve and the fact that they are aging and the idle adjusting mechanism may not move as smoothly as when new. One of the forum members cautioned against using a harsh cleaner to clean the ICV (I believe they melted theirs with carb cleaner or brake cleaner or something of the sort.) So look for that thread before you spray anything onto the ICV.

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[unknown4u]

I must say. The idle is as solid as a rock.

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[pdxmike]

Youve got the only one! These things idle all over the place. Im moderately convinced they did so from the factory. They use a very early implementation of electronic idle control, and the response time of the ICV is just not sufficient to keep the idle perfect.

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