420 SEL - Rough idle after valves replaced.

Need some repair advice. Story a bit long...

Local repair shop replaced my timing chain, rails, etc, as normal maintenance, but didn't do it right (chain didn't break, but slipped or something), resulting in 3 bent valves.

They agreed to do the repairs under warranty, but had problems getting it (engine) back together (broke head bolt by over torque, other miss-cues etc, requiring more waiting. They had the car over 3 weeks.

After many delays and poor customer service (never calling me and repeated promises to have the car ready were unkept), they finally got it running.

I picked the car up yesterday and the idle was so bad I had to take it right back, and asked them to repair. After picking up this evening, the guy said "some vacuum tubes needed tightening".

I drove it later this evening and there still is the unmistakable rough idle/surge at around 700-900 RPM. After that, the car is smooth.

The shop involved isn't very cooperative now and they have me really tee'd off. I suspect they've lost a ton of money on all the labor cost trying to fix the problem they created.

They are now trying to say its probably other maintenance items such as distributor cap or rotor, etc. I'm skeptical since the car idled fine prior to their valve re-work. I don't want to give them any more business than I have to, but I want the car fixed.

Anyone with repair knowledge of the 420 have some ideas on this? Could it just be a "fine tune" adjustment with timing or something vacuum related that is needed? Or something more ominous with how they handled the valve job, etc?

Any thoughts?

[fredsegal]

It sounds like you are living a nightmare. You were just trying to do preventative maint and end up with a real problem. Where is this horrible shop? If you let us know what area you are in maybe someone will recommend a shop that can give you an impartial diagnosis. With a real understanding of your problem you can better decide how to proceed.

FredSegal...

It's in Vancouver, Washington, just north of Portland Oregon. I'd mention the name of the shop, but I'll refrain for now until I get to the bottom of the problem.

They were registered with the Better Business Bureau and seem to have a lot of clientele, so they seemed "OK". It is an indepent shop, which I admit saved a few hundred dollars over the local dealer quote. But boy I wish I had ante'd up now.

Some examples of the poor work they've done:

1) Forgot to put the gas cap back on after the initial repair, resulting in gas in the overflow tube going all over (including my garage floor).
2) Didn't tighten the air cleaner wing nut at all, was almost ready to fall off.
3) Did something (still not clear on what) incorrectly with how they put back together a sprocket of some kind (so they say), which resulted in timing problem and resultant bent valves.
4) Broke a head bolt on the attempt to warranty repair, which they say they've replaced (reason for part of the delay).
5) Promised the vehicle to be ready 4 times, only to not call back to inform it really wouldn't be ready.
6) Resisted giving details of what the problem was and what they did to fix it. Said their "computer was down". (However, I did get a summary this morning, finally).
7) And of course, they can't get the idle right and act like they really don't want to fix it.

And yes, a living nightmare it is. They end up causing the damage I was trying to avoid by maintenancing the chain and guides.

That is why I'm worried about the rough idle. Could it be related to the valve job (said only needed "sent out" for one side only) or the over-torque?

Admittedly, I don't trust them....

Sounds to me like you should get an independent assessment of the problems, even pay a dealer to check the vehicle over so that if there is something wrong with the car that the original garage caused you will have clear proof. Then you can seek compensation or can get the repairs effected.

Good luck.

Matt.

[Rich126]

Sounds like a nightmare, but - if you payed by credit card, it doesn't have to be.

If you did use a credit card:

First, try and get them to fix the idle, get a receipt or some proof that you gave them another try.

Get an expert opinion - estimate from a dealer to REALLY fix the problem. Dispute this amount of the charge from the old repair with the credit card company. If the new estimate is higher than what you paid already, dispute the whole thing. They'll side with you and the shop will be out the entire amount.

[sixto]

With the relatively low torque values of MB heads and the special tool that only allows 90-degrees of rotation at a time, it takes a real idiot to overtorque a head bolt. I suspect someone tried to put a long head bolt in the wrong location.

I doubt valves are the issue if it smooths out beyond idle. A compression test should tell you if the valves aren't seating properly.

How does the economy/vacuum gauge respond to the rough idle?

Sixto
91 300SE
81 300SD

Rich126..

The original timing chain replacement was paid by check a month ago. As to the repairs to their goofs, they are not charging for that. That is the ONLY reason I keep leaving it there to get repaired.

Sixto...

The economy gauge doesn't fluctuate or anything unusual.


There is now more to the story. This morning on the way in to work, the check engine light came on. Car still running, but not something I wanted to see.

So I'm wondering if its a fuel mix problem and/or something they screwed up with the emissions upon putting it back together?

[sixto]

It's apparently a simple matter to decode the check engine light. You press some buttons near the ECU and count blinking lights. There's a website that describes the process, but I can't remember the URL. Anyone have it?

Sixto
91 300SE
81 300SD

[sixto]

Steve Brotherton has an excellent article in the DIY section, but there's nothing specific to a 91 420SEL. http://batauto.com/MB.html is the website I was thinking of. It doesn't have any V8 engine codes. It also doesn't describe how to check your car without tools.

I took my SE to the dealer when the check engine light came on. The advisor pressed some buttons on or near the ECU, read code number and claimed it to be the air temperature sensor. Sure enough, I had started the car with the air temp sensor disconnected. It was a similarly simple matter to reset the ECU without disconnecting the battery. No charge.

Sixto
91 300SE
81 300SD

WE RECENTLY DID A VALVE JOB AND TIMING CHAIN ON A 500SEL AND ON COMLPETION IT IDLED SO ROUGHLY WE THOUGHT IT LEAP OUT OF THE ENGINE COMPARTMENT.
AFTER MANY HOURS OF RECHECKING OUR WORK(WHICH TURNED OUT PERFECT) WE DISCOVERED THAT ONE OF THE AIR DISTRIBUTION PIPES WE INSTALLED WAS PLUGGED ON THREE OF THE FOUR NIPPLES.
WHEN THE ALREADY NEW PIPE WAS REPLACED WITH ANOTHER NEW PIPE THE IDLE WAS PERFECT.
HOPE THIS HELPS!