Lets talk ICV...in detail this time.

[PASHAT]

I am having a problem getting my car to run properly, tied to my ICV in my 1991 Passat with a CIS-Motronic ECU. When I drive it I get hesitation, jerking, not running smoothly. Sometimes I seem to get it going well, but the problem recurs. Every time I pull the temp sensor harness when it is obviously running rough, the car runs fine.

The temp sensor was quite new. Although I put it in last fall, I have only driven about 175km on it.

So, I start to thinking, what could be controlled by the temp sensor that could cause surging. I start thinking ICV. Hmm. I replaced that with a used one that opened and shut without problem when current was applied. Time to look closer.

I pull the ICV and replace it with a 3/4 plastic pipe elbow. Fits pretty good. I leave the harness connected and start it up. Car starts up pretty fine and idles not too bad. I give it gas. I watch the valve inside, that is currently closed, and it doesn't move. I try again. No movement at all. Car is warm, and running well with my equivalent valve apparently open (because there is just a piece of pipe there). I connect a spare harness to the ICV, touch it to the battery and the thing snaps open.

No power from the ECU to the harness? I get out my little multimeter and give it a test. Sure enough, the harness connector for the ICV HAS 12v. But when *I* give the ICV 12 volts, it moves fine. When the ecu gives it 12v, it doesn't move at all.

Is it a lack of amps? Faulty ECU? Faulty ICV?

I tried another ICV that I have, that is very similar but for a Volvo. Same thing. Snapped open when I gave it 12v, but did not respond at all to the harness, where I was measuring 12v.

I tested the resistance on each of them and I got 8.1 ohms for the one that is for my car, and 8.3 ohms for the one for the volvo.

When I did the pin to harness test of the ECU to ICV in Bentley, it checked out fine.

Oh, and when the pipe was in place and the ICV was out, the car, as I said ran fine. When I disconnected the ICV from the harness...remember this ICV is not connected to the car in any way except for the harness, the car starts that surge and slow down repetition thing going up and down about 200rpm in rapid succession. When I reconnected the ICV the surging continued. I had to turn the distributor cap counter clockwise to get it to slow down. Not sure if that is a knock sensor issue.

How can the ICV open when I give it 12 volts, but not open when the car gives it 12v

I took the car for a test drive without the ICV in and it ran fine, so I am sure that I have found the problem finally. I am just not sure what I have found.

Can anyone explain any of this to me. I don't see a good test for the ICV in the Bentley.

I have been working on various aspects of this car for a year. Like I said, it has been driven only 175km over that year. I would REALLY like to get this resolved and I know that I am close.

Any help would be appreciated.

[rjc69]

Sorry, don't run one....Don't like the concept of having an extra valve(more wiring)on my engine..Using MSII, don't need it.......
OK,
1: by bypassing the ivc with the pipe, you increased air flow at idle(car has 2 switches on the throttle body-1:closed/2:wot)when the throttle is closed, the ecu knows this and monitors air flow and adjusts air flow through using the icv. Thus by bypassing the icv with a pipe you told the ecu that the engine was getting too much air and it was trying to close the icv.
2: Proper operation of ICV.
The ecu uses the ICV to maintain a smoth idle when the engine is below 300rpm AND the throttlebody is in the closed posotion.
This is the only time the ICV is used under warm engine conditions....
3: the symptoms of a bad ICV
DOES NOT IDLE WELL, OR AT ALL ONCE WARMED UP!!!!!!!

Trust me I chased a bad ICV before, it's why I won't eVER run one no that I'm on a standalone......
Look else where for your problem.....Rob......

[PASHAT]

Thanks Rob. You have no idea how much I have valued your input on many issues.

I too, am going to MS on my Scirocco due to a year of misery with Motronic.

Makes sense that ECU is trying to close the ICV, but why is it sending voltage to it? With the ICV out there was voltage at the harness for the ICV. I should try blocking the rubber pipe by squeezing it and see if the ICV responds.....It should, shouldn't it?

I am starting to wonder if it could be my closed throttle switch. Maybe it is not sending a closed signal at the right time so the ICV never operates. (Oh wouldn't that be rich...a certain texer would rightfully never let me live that down, would they). I did check the continuity of this in the ECU pin test, and it was fine.

Quote, originally posted by rjc69 »

Look else where for your problem

I am not sure that there IS an elsewhere. I have been through this engine everywhere I can think of....remember I have been at this for a full year, come September.

Below 300RPM? Is that a typo?

BTW, I found this thread useful, except it never ended satisfactorily:

http://forums.vwvortex.com/zerothread?id=1012485

[vwsickness]

I recently chased some idle problems with my 91 Passat and I'll share my experiences just in case any of it can be of use. The car is a 1991 Passat GL Automatic Transmission with 127K miles on the clock. VAG-Com scaned and there were no faults stored in either engine or transmission ECU's. The issue at hand was that 50% of the time the car would stall as it was coming to a stop. Over the course of three days the problem became progresively worse and I could get the car to stall by simply letting it roll downhill in neutral and stabbing the brake. If I slowed the car gradually it would typically not stall. Power and acceleration were "normal". The idle was erradic and at times would hunt between 800-1400rpm. Unplugging the ISV would make the engine hunt 800-1800rpm and would not stop. I also tried unplugging the O2 sensor with the ISV connected and this would also make the idle hunt but the car would not stall quite as much. Checked for air intake leaks and found none. Checked idle switches and they were adjusted properly and performed as described in the Bentley. I replaced the transfer pump as it seemed like a fuel starvation problem in regards to the rapid decleration stops. The transfer pump was original to the car and upon replacing it the car no longer stalled by rolling in neutral and rapidly stopping. 40% of the problem solved. Also gone was the hunting idle when both O2 sensor and ISV were connected. Now the problem that remained was the idle dropping to the point of stalling when coming to a stop. Also if you tap the accelerator quickly and back off, this would guarantee a stall in both drive and reverse. At this point I hooked up the VAG-Com in the measuring block mode and noticed that the working value for the ISV was out of range. The O2 sensor was also at the range limit as well making me think it was likely going south as well. Since it pains me to spend anything more than $5 on this car I focused on the item which was out of range...the ISV. Called my local parts place and just about fell out of my chair when they told me the list price and "my price"...$440 and $327 repectively. Ebay to save the day....I got a used ISV and two minutes after installing it....I had a normal car once again. Idles perfect and cannot get it to stall let alone hiccup. The best part of all is that this car has more power than it ever has under my ownership (60K miles). My old ISV had a resistance of 8 ohms while the replcement ISV holds a value of 8.9 ohms. I also connected the VAG-Com and the working value of the ISV is now within the range of acceptable values.

[vwsickness]

Quote, originally posted by PASHAT »

Makes sense that ECU is trying to close the ICV, but why is it sending voltage to it? With the ICV out there was voltage at the harness for the ICV. I should try blocking the rubber pipe by squeezing it and see if the ICV responds.....It should, shouldn't it?

I looked at the wiring diagrams and it apprears that the ISV gets a 12v constant and the Motronic supplies the variable ground to control the ISV opening

[PASHAT]

Quote, originally posted by vwsickness »

I looked at the wiring diagrams and it apprears that the ISV gets a 12v constant and the Motronic supplies the variable ground to control the ISV opening

Bingo.....I forgot this little tidbit. Explains a lot. THANK YOU all for taking the time to help.

With ISV bypassed and temp disconnected, car runs fine. With temp sensor disconnected, and ISV connected, car runs fine. The temp sensor is new. ISV responds to 12v. With both connected, car hesitates in the midst of acceleration, dies sometimes, unequal acceleration.....

= ECU is not grounding ISV consistently UNLESS temp sensor is disconnected.

Why is the car running rough???

I will retest the continuity of the ICV to ground and see what happens when I squeeze the hose where I have the pipe bypassing the ICV.....

Any brilliant (or less so) ideas of what might be occurring?

[PASHAT]

Quote, originally posted by PASHAT »

I forgot this little tidbit. Explains a lot.

Argghh! Wait a minute....I was testing for voltage at the ICV harness and it read 12v. Regardless of whether the ECU controls voltage out, or the ground on return, it HAD 12v at the harness....so the ECU was giving a ground.

[vwsickness]

Sounds like the ECU is trying to fully open the ICV as the ground should change depending on what the ECU wants to do. I'll see if I can tap into the ISV harness while it is running to see what resistance to ground I have.

[PASHAT]

Quote, originally posted by vwsickness »

I'll see if I can tap into the ISV harness while it is running to see what resistance to ground I have.

mAmps might also be interesting. I will also check my ground resistance at the harness.

[shryocdj]

i wont say a word, especially since it probably wasn't the problem

wish i could help more
keep at it man, you'll get it sounds like you're constantly making progress

[PASHAT]

Quote, originally posted by shryocdj »

i wont say a word, especially since it probably wasn't the problem

You know, I hate it when you are right......especially when it was me that helped you with that switch issue! (And it isn't the switch either!)

And I still honestly don't know what it is.

Here is what I found.

I went out and started the car...3/4 in pipe in and ICV hooked to its harness and out. Car was cold. Started it and basically did the same thing that I did yesterday....no response at the ICV. So I took the ICV out and gave it 12v....it snapped open. I put it back in the harness and pinched the hose until I could hear the engine really start to fade. No change...ICV stayed shut. So I check the harness....it is pumping out 12v. I check to see which is hot and which is ground and it is the WHITE wire that is hot, and the black wire with the (white?) stripe that is ground. I check and white wire has 12v to ground. I check the black wire and I got some different readings on continuity I think due to bad connections, but eventually it clearly gave me 0 when I went between that pin on the harness and ground.

So, we have 12v coming in and continuity to ground going back. Seems like ECU wants ICV open, but it ain't opening when I connect it.

So, I go and look at the closed throttle switch. I open it and can hear it click. What the hey...I disconnect it. Engine starts to run really rough...disconnecting it would tell the ecu that the throttle is open when it really is shut.

Then all hell breaks loose and the car starts to run really rough and backfire and sputter and start, and then it dies. I get in and try to start it.....won't. Now I am going what the heck. Was there some weak component that just caved (and I am secretly hoping so so that it will finally reveal itself....) Anyway, turns out it was just out of gas.

I reconnect the harness for the closed throttle switch, and the car runs better. In fact it gets pretty smooth and I am thinking it is running better.

So I go back to the harness and do more tests. 12 v in. I check the negative wire for continuity to ground, and I don't get 0 anymore....I get -12.1. WTF? How can you have negative ohms? Then I realize that I forgot to change my multimeter to ohms and I was still on volts. But, WTF(2)? Why am I getting NEGATIVE volts when I am going between the negative ground wire and the NEGATIVE terminal on the battery. I mean, if I just switch my leads around, I will have 12v between a ground and a ground.

Methinks that should not be.

What are you all thinking the problem is. Are you thinking what I am thinking. Is there some sort of short in the ECU that is causing it to have + current going through a negative wire. Bad Ecu! BAD ECU!

I have a spare ECU that I use to test as I know the car has run fine with it. So I pull that out and plug it in. I plug in the ICV in its harness and wait for it to begin ticking properly. Engine is idling nicely with the 3/4 pipe. ICV stays closed. I rev the engine. Still closed. Absolutely no different than with the other ECU. So I REALLY pinch off the hose, to the point where I kill the engine, and....JUST before the engine dies, that ICV yawns wide open. It appears to be working.

I plug the original ECU back in and repeat the same test and get the same result...JUST before the engine dies, she opens wide.

What have I learned? I learned a good test for the ICV. I learned that once again, Rob was right in his suggestion that the ICV was not the problem (more on that later). I learned that Shryocdj is also right in that if all the ICV does is open just before the car dies to give it more air, it really isn't THAT important in the running of the vehicle, and we blame it too much for other issues.

I also learned something that I think is critical. The ICV is normally closed. This is very important to me because remember that my car runs either with the pipe in place (which would be an OPEN ICV) or with the temp sensor disconnected (which would signify a COLD car).

When the ICV opens, does it increase air or fuel?

Oh, and the reason it doesn't open when there appears to be current there, and why I get voltage on the negative side....I believe that might have to do with "duty cycles".

[shryocdj]

i wasn't trying to be a punk; i really believed the switch wasn't your problem

and I give you mass props for being so diagnostic and figuring all this out.

[PASHAT]

Quote, originally posted by shryocdj »

i wasn't trying to be a punk; i really believed the switch wasn't your problem

I know...and I appreciate all the support and input you have given me. I am cheeky as anything....not to be taken seriously

Quote, originally posted by shryocdj »

and I give you mass props for being so diagnostic and figuring all this out.

Wish THAT were true.

Note: In another post Volks25 pointed out that one should never disconnect the ICV when the ECU has power to it as it could damage the ECU. I put that here for anyone who is reading this in the future.

[shryocdj]

i know you were talking about timing before and how advancing it would crap out your idle?

well i remember this website says motronic should be 6-8 btdc....
http://members.dslextreme.com/....html
towards the bottom.

now that being said, i remind you i know nothing

just pointing it out in case it might help (i didnt reread the thread/post, so I may be way off)

[dublife1992]

well did u get anywhere wit this?