Weird running issue.

[sebastian kach]

So I have the timing set at 12 degrees advance at idle. Idles around 900-1000. When driving the car cold or hot it hardly wants to get out of its own way until warmed up except when I stand on the pedal and the full throttle switch is hit. When it warms up to reg operating temp the studder and uneven acceleration is better but not quite right. But when I go full throttle it runs awesome and pulls hard and smooth. Any advice.

[Fat Rabbit]

You need to tell us more about the car. VW used several injection systems over the years and numerous modifications to those systems. FR

[sebastian kach]

86 CIS. A mouse chewed on the O2 wires so to eliminate that as a source I just unplugged it last night and it seemed to run the same, maybe 10% better. I am wondering if the injector spray pattern is bad enough if it wouldn't cause this issue under mild accel and when it goes full throttle it doesn't matter. Also ran the same way with the knock sensor harness chewed up and basically gone. I now have the knock sensor harness repaired and installed on the car. Has anyone experienced this sensation with a malfunctioning knock sensor?

[Fat Rabbit]

Since you suspect the injectors why not pull them and inspect them. While you are at it replace the injector O-rings.

Also look for vacuum leaks - search Vortex for places to look.

Replace the O2 sensor.

FR

[Esevw]

So I have the timing set at 12 degrees advance at idle. Idles around 900-1000. When driving the car cold or hot it hardly wants to get out of its own way until warmed up except when I stand on the pedal and the full throttle switch is hit. When it warms up to reg operating temp the studder and uneven acceleration is better but not quite right. But when I go full throttle it runs awesome and pulls hard and smooth. Any advice.

Isn't timing supposed to be set at 6 degrees before tdc?
Recheck your timing.

[sebastian kach]

Timing is supposed to be at 7, others have said they run more than 12 with no problem. I ran it at 7 and it didn't gain any lower end and it didn't have the strong top end either obviously.

I am only going to pull injectors as a last resort because I did have to replace one already because it had a dead cylinder and it was a fiasco. It broke off in the manifold and fell into the port and I spent a few hours extracting that. I know I should just remove the manifold and probably replace them and the cups and seals. I am just curious if anyone has experienced anything quite like this and what they came up with. Thanks for the suggestions guys.

I'm kinda leaning toward the O2 as a source of the problem since when hitting the WOT switch it runs awesome and thats when the system goes into open loop and ignores the O2 altogether.

[rabbitnothopper]

so what youre saying is the car needs more fuel.

thus

vacuum leak

[sebastian kach]

So I checked for vacuum leaks. There are some around the injectors, not horrible but they're present. Today I checked for activity from the O2 and there was none. Went one step further and grounded the green wire which is part of the car harness to the fuel ECU thus making the car run at full rich and it runs awesome no matter what throttle position. Diagnosis is to replace O2 sensor. I may just drive it like this and see what the MPG's are before I get an O2 sensor. Probably will remove intake and replace all of the injector seals as well, but for now, I'm pretty happy.

[Rhrsbg Equipt]

So I checked for vacuum leaks. There are some around the injectors, not horrible but they're present. Today I checked for activity from the O2 and there was none. Went one step further and grounded the green wire which is part of the car harness to the fuel ECU thus making the car run at full rich and it runs awesome no matter what throttle position. Diagnosis is to replace O2 sensor. I may just drive it like this and see what the MPG's are before I get an O2 sensor. Probably will remove intake and replace all of the injector seals as well, but for now, I'm pretty happy.

hello, im having a similar problem with my 79 1.6 8v.. when you say o2 sensor are u refering to the aux air valve on the back of the intake?, ive never herd the terminology o2 sensor on the cis motors and am just alittle confused. thanks!

[sebastian kach]

O2 sensor= oxygen sensor, which is in the exhaust downpipe. It reads the air fuel mixture essentially and tells the ECU to either enrichen or lean out the fuel mixture. I'm not sure if the 79 has an O2 but if it does its just a one wire sensor making it easier to test as I did mine.