Drove my '99 vanden Plas home for lunch. Absolutely no problems (ever) with the car. Upon leaving to return, the car slightly drag when the starter was engaged, but it started but the engine was running incredibly roughly. No Check Engine light or display in the heads-up area. Shut engine off waited a minute and restarted. Engine again started, no hesitation but still running ridiculously roughly. shut down. I first thought it was some type of ECU malfunction, but now I am leaning more toward timing chain (belt) or something internal, but to break during starting seems a little odd. What does everyone think and how would you begin diagnosing the problem?

 

Please DO NOT start the engine again. Your post doesn't say but unless you know for certain that your secondary timing chain tensioners have been changed that is the 1st place to start. If it is the tensioners you are 1 re-start from bending some valves or destroying your engine (redundant).

The tensioners are covered in this forum extensively - a search will provide many hours worth of reading on the topic.

 

The very first thing to do is a visual check of all the intake piping and vacuum hoses, full and part-load breather, etc. Rough running could be as simple as a vacuum leak. Second, by "starter drag" I assume you mean it turned over slowly. That sounds like a weak battery. You won't be able to visually diagnose that but certainly electrical issues could cause it to run rough too. If you are not sure the secondary tensioners have been replaced, I wouldn't try starting it again without further diagnosis, but it may be worth having the battery tested. I would expect it to throw a code if it was running that rough but stranger things have happened.

 

Skipping a tooth due to tensioner failure will cause rough running but not throw a code. Do not try to start it again until you check the tensioners.

 

It's possible that the slow drag on the starter was the tensioner 'shoe' jammed between the chain and sprocket putting a strain on the starter. Maybe the chain broke, maybe it did not.

bob gauff