Rough idle after valve adjustment ('84)

andy_braselton · 06-13-2020, 03:25 PM

I am a little new to the 911 world and this is my first valve adjustment so feel free to let me know what I did wrong.
My 1984 911 was running pretty good but my mechanic suggested a valve adjustment based on the clatter from the valves that he was hearing. I wanted to try this myself so that's what I did. I took my time and changed to oil and spark plugs at the same time. I used NGK Iriduim plugs and did gap them according to the Bentley manual.
After the valve adjustment I put about 7-8 quarts in the car and started it up and then slowly added another quart or so.
The car ran rough at idle after start up. I gave it some gas and it hesitated to pickup and even popped as I let off the throttle. It did rev to about 4k. I chased down all the spark plug wires and they are in the correct position.
Is there a startup procedure for after changing the valves that I don't know about? The car was not at TDC when I started it.
I don't know when the previous valve adjustment was done. I was wondering if it is possible if the car's timing and even fuel mixture has been adjusted to compensate for a poor running car due to valves being out of adjustment and after I adjusted the valves the car is not in sequence.
I immediately thought the timing may be slightly off but after a little research in the manual I realized the timing is DME controlled and can't be adjusted at the distributor. The Bentley says it can be checked with a light but gives no other info. Could this be timing still? Can a shop adjust this?
My second assumption is possible fuel mixture to lean. The spark plugs I pulled out had white residue on them which I understand indicates lean running.

Let me know what you think, all suggestions welcome.

DWeg1998 · DWeg1998's Garage

Double/Triple check the wires on your cap. Make sure the distributor cap is fully seated and in the correct position.

What method did you adjust the valves? I’ve screwed up before by tightening beyond zero lash then loosening from there. Did you feel each rocker that there is some motion after adjusting? Could debris have fallen in your plug hole in the valve gap?

andy_braselton · 06-13-2020, 06:55 PM

I’ll check the cap again. I did have trouble getting it back on. I use SnapGap to do valve adjustments which is pretty accurate in getting gapping correct but I’m sure there is still a chance I screwed it up.
I’ll check it again.
Thanks

RedCoupe · 06-13-2020, 08:19 PM

If your 911 ran okay prior to your recent work, then chances are that something you did is causing this. More than likely, you will find that one or two cylinders have valves that are not closing completely when they are on the back side of the cam. If you wind up pulling the valve covers to recheck the valves, if you jack up one side of the car at a time, you can prevent spilling your new oil. Also, you can get a feel for what a properly adjusted valve feels like when you move the rocker arm, so you shouldn't have to use the feeler gauge to see if a particular valve is adjusted too tight. Obviously, you still have to turn the crankshaft over as you work through the firing order, but you shouldn't have to use a feeler gauge on every valve. Another idea is that something was pulled loose when you were doing the work. An injector electrical plug or a vacuum hose, perhaps?

mo-mon · mo-mon's Garage

I assume you used spark plugs with the proper heat range for your '84. That said, check the wires from the plugs to the distributor cap as Dweg1998 suggested. Make sure they're properly seated. Check the cylinder head sensor (the white one) just in case it got loose.

No special start up procedure here. I bet it's probably the distributor cap or rotor. Did you replace them? If so, Bosch or Beru?

gomezoneill · gomezoneill's Garage

Adjusting the valves on these engines is not a good idea for the inexperienced.

pete3799 · pete3799's Garage

Are you sure you were on TDC when you started the valve adjustment?

stlrj · 06-14-2020, 05:06 AM

" let me know what I did wrong."

Post a picture of your distributor cap. We might be able to tell if you got your wires crossed.

wareaglescott · wareaglescott's Garage

Quote:

Originally Posted by gomezoneill

Adjusting the valves on these engines is not a good idea for the inexperienced.

This sure is a helpful post! lol

Good for you OP for giving it a shot. You can learn a ton by doing it yourself and will get it straightened out.

911obgyn · 911obgyn's Garage

Perhaps old plug wires. They have to snap on to the plugs,sometimes the resistor in the wires comes loose. Another thing to do while you have the cap off the distributor is check the play in the shaft and put a drop of oil under the felt in the shaft where the rotor attaches. Valve adjustment is one of the things every owner should do at least once, just to know how it’s done, it is not rocket surgery!

NYNick · NYNick's Garage

Go over everything again. I would especially make sure your wires were reconnected in the correct order, again. Did you remove the rotor? Did you take a picture of the distributor and the wire placement before you started? Have you traced the wires from the dizzy to the plugs to make sure they're in the correct places? Have you pulled the plugs and checked them? Are you sure they're connected correctly to the wires and 'snapped' in place? Are your plugs torqued properly?

It sounds like ignition issues to me, not valves. When I did my valve adjustment for the first time, I did them twice. Once to learn how to do them, and the second time to make sure I did them correctly.

andy_braselton · 06-14-2020, 07:56 AM

Thanks guys,
I will start by again checking the wires and the cap. Ill also check injectors, maybe one got bumped. I agree that it sounds like ignition issues so I will start there. I will also double check the heat rating on the spark plugs.
I'll let you know what I find.

Thanks

andy_braselton · 06-14-2020, 11:13 AM

Jacking the car up on one side and tipping the oil to the opposite side of the engine is a great idea. If I take the lock nuts off can I reuse them and the washers or will they have to be replaced?

NYNick · NYNick's Garage

Quote:

Originally Posted by andy_braselton

Jacking the car up on one side and tipping the oil to the opposite side of the engine is a great idea. If I take the lock nuts off can I reuse them and the washers or will they have to be replaced?

You can reuse them, but the gaskets are another debate. They come with the gaskets from our host anyway.

andy_braselton · 06-15-2020, 01:22 PM

The cap looks tight and the number 1 plug is facing the fan shroud like it should so I think I got that in order. I realized I had one plug in the 4 cylinder that was still a Bosch plug. I replaced it with an NGK like the others. Cold start up was a little better but it still took 20 seconds or so to get to an idle of about 900-1000 rpm where it usually warms up at. Giving it throttle was a little smoother this time. Bottom line, the car still seems rough but slight improvement based on plugs. I am beginning to think the car doesn't like the plugs I put in I gaped or the heat range. The plugs are NGK Iridium IX BPR6EIX 6637. I gaped according to the Bentley Manual between .028 and .032. I split the difference and did .030. The heat rating on these plugs is a 6. The car had Bosch WR7DC plugs gapped at about .040. These are Copper plugs. I am beginning to think the plugs are too high performance for my car. Any experience with Iridium plugs in these cars?

Crude Rudy · Crude Rudy's Garage

About the same thing happened to me the first time I adjusted with Snapgap. Only thing I changed was valves so I went thru them again and guess what, two were f'ed up. Reset them and now she has never run better. And I have done the valves myself for 20 yrs on this car with no issues. With the valves set exact with Snapgap it should run great, as suggested jack one side at a time and the next day set those 3 again, just like starting from scratch with new shims. repeat the process

brshap · brshap's Garage

Quote:

Originally Posted by Crude Rudy

About the same thing happened to me the first time I adjusted with Snapgap. Only thing I changed was valves so I went thru them again and guess what, two were f'ed up. Reset them and now she has never run better. And I have done the valves myself for 20 yrs on this car with no issues. With the valves set exact with Snapgap it should run great, as suggested jack one side at a time and the next day set those 3 again, just like starting from scratch with new shims. repeat the process

I thought snapgap made it impossible to have a the clearance wrong. Could you elaborate a bit as to what went wrong? I was thinking about getting snapgap.

Crude Rudy · Crude Rudy's Garage

It does but not if you/I get TDC a bit wrong. Snapgap was not the issue, operator error was the cause .... probably cause I only lifted and adjusted one side at a time cause the oil was new

andy_braselton · 06-16-2020, 01:01 PM

I figured it out with you all helping me. The number 3 exhaust valve had no play. I had trouble when setting it and was suspicious it might be a problem. SnapGap works great. The problem was the threaded stud on #3. The threads didn't want to accept the new jam nut like it should have. I should have checked the play before moving on. The .10 mm is so small that it can be tough to recognize. Thanks for the help.

JohnTucker · JohnTucker's Garage

Great vid about valve adjustment. I thought it was pretty remarkable how many attempts it took her to get it right. Impressive effort:

https://www.youtube.com/watch?v=6ciw3mDjz0k