engine bucking low rpm and throttle

I posted this in the tdi 101 but got no chimes on it. this is a 91 corrado that has a 98 jetta tdi full swap. engine is running great getting 44 to 45 mpg. plenty of power also. I had the timing checked on the vag and it is good. no engine codes. at light throttle at 1500 to 1800 the car will buck pretty bad. you have to either let off the throttle or give it more then it will go away. could it be the throttle position at the gas pedal going out? if so should it throw a code. soon as I get this issue resolved it will go up for sale. it is my daily and that is the only issue

I've read of people cleaning the MAF sensor to cure various running problems. Have you checked the tdi faq.

Mine does the same but i cant get it to rev any higher than 2100RPM and i still can't figure it out

cleaned the MAF no change. it looked real clean. you can hold it steady at 1500 rpm out of gear and it is smooth. it seems like the tps has a bad spot in it near 1/8 throttle. I am going to try and ohm it out with a analog meter and see if it has a clean sweep from closed to wide open

Timing?

I post this at the risk of being wrong and knowing that you said that you already checked it...

With my '97 TDI, the timing causes this exact problem.

If I get to where I'm going to "lug" the engine, at say 1400, or 1700 RPM, and I *slowly* give it gas, it will buck and shutter if the timing is off a little... the timing on my car tends to migrate "down" the graph over months and thousands of miles.

Another indication of the "problem" is that when it is cold, the car is a little harder to start, and puts out a puff of white smoke immediately after startup. It shutters a little, then settles down.

In the past, if I change the timing to be "just above" the blue (center) line, then this fixes my problems.

I find that I need to do this about 2 times per timing belt.... say every 20,000 miles.

My vehicle must be sensitive to this slight change (stretching of the timing belt) in timing...

I would say that it would be worth "playing with" different timing settings in your car, to see if it fixes things.

I could be wrong, but I hope this helps....

Chessie

sounds like something worth looking into. symptoms are the same here except it will fire up great even in the morning when cold. thank you for the info.

I had the same problem on my '98 Jetta. Turned out to be a timing issue. At the same time, I needed a fuel pump reseal job done, so I brought it to a mechanic who resealed the pump. Part of his job was also adjusting the timing after doing the reseal job, and that fixed the bucking. I struck two birds with one stone.

I started this thread concerning your bucking problem several months ago:
http://forums.tdiclub.com/showthread.php?t=279953