1986 8 valve head on 1993 2.0 L short block running issues

[AndyMan7778]

Hello, hopefully someone can help me with this. I installed a 1993 Jetta 2.0 liter short block under my 1986 Golf Gti head. I researched the swap, using the A3 timing belt and the distributor mods. The engine runs like a scalded ape. The head has been rebuilt. I have a new fuel pump, new accumulator, a new set of injectors, and a new differential fuel pressure regulator. I have 76 psi while running at the fuel distributor, and the system holds 38-40 psi residual pressure as it should.
The problem I am having occurs at partial throttle from an idle position when I am just maintaining speed like on the highway. The engine will cough and sputter and buck wildly, making the car jerk forward and back like crazy. Then, if you stomp on the throttle, it will run hard and smooth as long as you are under hard acceleration. Then, if I back off and maintain speed, it will do it again. I have zip tied the high speed throttle body switch closed and that makes the car drivable, but it still surges slightly when maintaining speed. Again, if you accelerate hard, it flies with no problem. I have tried a different fuel distributor and it runs the same.
This is my 15th VW I have owned in the past 20 years, I started out with a 79 Rabbit diesel, so I am no stranger to the strange things that our Dubs do sometimes. Anybody have this problem with an ABA block swap into an A2? thanks

[Jones84]

I have done this set up a few times, Most of the time I do a Digi2 system with it. When done and running right it makes a good Strong 8v.
Have you tried Using the 2.0 16v fuel distro? then tuning it with the Allen to get the fuel just right?
I would get a 02 gage or a wide band so that you can see what is going on.

[AndyMan7778]

I think my other fuel distributor is from a 9A 1.8 16 valve and like I said in the previous text, it runs the same. It's weird, I also noticed that it doesn't do this problem while it is cold, only after it warms up. I don't really want to switch the fuel dist. to a Motronic, but this situation is getting old. I mean, the car runs great, other than this. It has 340,000 miles on it and I don't want to quit driving it. It gets 29 mpg and handles like a BMW. If I use a 16v dist. does it have to be the Motronic with the electronic injectors? If I do that, I have to switch the whole engine wiring and computer and all that don't I?.. It acts like it is getting too much air but I haven't found any leaks. If it was ignition or valves, it would do it all the time, not just at over idle. I replaced my brake booster when I did my master cylinder just in case that had a hole it it and was sucking air and no difference. What type of O2 gauge do I need for this and what is wide band? A mechanic buddy of mine is going to help me with this and the better prepared I am the better. I REALLY APPRECIATE YOUR POST, thanks, Andrew

[Jones84]

You can get any one wire gage that reads 02. I think your local Auto parts store should have one or be able to get one for you.
A wideband would be best. but not needed with CIS.
You could take it to a shop that has a dyno. they will have a wideband and can tell you whats going on. If it is a air fuel thing.
It sounds like it might be a ISV issue.

[Rannoch]

Your clue should be that it only does it when it's not cold. I bet the car isn't getting enough fuel at half-throttle.

The Bentley manual for the fuel system (the car it came from) should give you an idea of what to look for.

I'd go through the Bentley and verify that the fuel system (including the coolant temp sensor) is in good shape.

[Jones84]

I'd go through the Bentley and verify that the fuel system (including the coolant temp sensor) is in good shape.

Nice, I over looked that one. Very good chance its not working Right.

[AndyMan7778]

Yeah, the other weird thing is that it only started doing this after I swapped to the 2.0 liter short block. Someone did say to me once that maybe the larger block when require more fuel, but I at that time I wasn't ready to fix the problem, I had just gotten the car running again.
Do you think a different O2 sensor, like from the A3 chassis would help? Is it sending weird signals to the computer maybe?
Which coolant sensor, the thermotime switch only controls the fifth injector, the one on the oil filter outlet is for the guage-I guess it would be the one on the bottom side of the water outlet on the front of the head.
Also, what is the "ISV" issue you speak of? I haven't heard that term. I do have the Robert Bentley book on this system, which is part of the reason I am able to keep it running. It is going to be that book that proves invaluable in the repair of this issue because of all the values and info it has in it.
Also, this is a CIS-E system. What is a wideband guage-does that read the exhaust O2 levels?
Like I said, a mechanic friend of mine is going to help me with this when we finally get to it and I am just trying to get some ideas before I use his valuable time..

THANKS AGAIN FOR YOUR POSTS BOTH OF YOU-Andrew

[Jones84]

The ISV is Idle Stabilizer Valve. It opens and closes letting in more air for cold start and helps to keep it idling right. But If not working right can cause a Lean issue.
Wideband is a 02. Used for tunning in allot of high performance cars, it will tell you if you are Rich or lean and were at so you can adjust or change to make it right.
They are about $200 or so. Not really needed with CIS. Just a 02 gage will tell you where you are leaning out at. You can get just the gage for about $30.

[AndyMan7778]

I am pretty sure my Idle stabilizer valve is working ok, it hums and such like it says in the manual. It has not been replaced with a new one yet. They are stupid expensive.
The engine idles ok, from about 900-1100 rpm depending on conditions.
My coolant sensor has not been renewed yet, that is the first thing I am going to check. What if I let the engine warm up and disconnected the coolant sensor connector-would that simulate a cold engine and richen the mixture?
What about differential fuel pressures and the pressure coming from the fuel pressure regulator?? Could it be one of those pressures? I read through the Bentley book researching all this and it sounds like I am going to have two weeks in diagnosing and repairing this problem.
Again, thanks a lot-Andrew

[AndyMan7778]

Did you guys ever find out any more on this?

[Jones84]

Did you ever hook up any 02 gage to see if you are leaning out any were? have you Done anything to try and solve the issue?

[AndyMan7778]

I am going to start with the Thermotime and coolant sensor circuits-I am just trying gather as much info before I get started because once I get into it I don't want to stop until it is fixed.
I will get an O2 gauge as well.
Thanks for your help I really appreciate it- Andrew

[buggyboy20]

Unplug the coolant sensor plug and take it for a spin...my mk2 had the same issues...if that works plug it back in and unplug the O2 sensor...again go for a spin...could be one or the other...check ALL vacuum hoses as well...get a can of quick start and spray them with it...if the idle changes at any point go back and check it again...that's all you may have wrong...as for the ISV take it off and fill it with WD40 and let it sit overnight...empty and spray it out with some air...DON'T USE BRAKE CLEANER OR THE LIKE...look at all the grounds...a small movement in the drivetrain could change the position of an important one when you mash the throttle and move it to a better position of connectivity...old cars=old wires

[VolksRacer2]

Check the simple stuff first...sounds like a classic vacuum leak to me. I'm aware there are other things that could cause the symptoms you describe, but I'd take a close look at all vacuum/intake stuff before spending any money trying sensors.

[AndyMan7778]

I have gotten into this problem a little bit. I replaced the injectors again, and the O2 sensor-still does it. I am wondering about the potentiometer in the fuel dist housing, the Bentley manual says the resistance has to be a certain value. This part is $700.00, so I am hoping that isn't the problem. I also replaced the coolant temp sensor under the water outlet on the head. I did also check my cold start valve operation and it doesn't squirt any fuel upon start-up, not that that has anything to do with driveability. I did check for air leaks, you think it would be something simple like that, didn't find any. The throttle body boot was sucking in a little air-when you sprayed wd-40 in there it would suck it slowly into the boot-not quickly. I spun the hose clamp and stopped that.

My next thing to do is hook up a tester to the differential fuel pressure wiring harness and go through the electrical values. And get an O2 guage. It seems to me that is where the problem lies, between electrical/fuel management, since this system relies on the electrical inputs from various sensors to alter fuel control. The thing I don't get is why this problem started after I installed the 1993 2.0 liter short block.

AGAIN< ANY HELP IS GREATLY APPRECIATED-THANKS!!

[AndyMan7778]

OK, I figured it out. I had the wrong Hall sensor in there. When I did the 2.0 liter swap, I used an A3 dist with the 4-window rotating part and that is what messed up my computer because it was always trying to alter the timing. So the moral of this story is: engine swap or not, keep all of the like components for the system you are running and don't mix them !!! Thanks!!!