My 71 Impala is idling erratically. What is the problem?

Question

It has been cold lately, so I went out to the garage to let my 71 Impala run and warm up a bit. It turned over ok but I noticed that it idles erratically and not really strong. I hit the accelerator a few times and the engine sounds good. I pulled it out and drove it around a bit and it runs perfectly fine, but when its in park it sounds funny. I was thinking about rotating the distributer a bit to see if that helps. Is there anything else I should check?

Im thinking its either the EGR valve, intake leak, or just bad timing. Anyone else had this problem with a 350 or 400 small block engine?

Answer 1

DON'T just go and turn the distributor - it controls your engine's timing and should only be set with a timing light. A '71 should not have an EGR valve on it. I suspect that you've either got a contaminated spark plug that is misfiring or possibly the fuel/carburetor adjustements are the cause.

Answer 2

Check the condition of your ignition leads, plugs and ignition system as a whole, including the points and condenser. First thing I'd look for is one or two faulty ignition leads. Condensation on the ignition? Could be that after you ran it a bit the idle came good, tho that might just have been the engine going off the choke. Rotating the dist may not help, but you can static time an engine with a 12 volt trouble light with no. 1 piston at Top Dead Centre. The plugs fire when the points open, and a 12 volt lamp across the points will light or get brighter at that instant. But that's the last thing I'd do.

Does it have an automatic choke? Maybe the choke isn't working as well as it could. Some older vehicle are not much good until warmed up, tho the one I'm thinking about was an early 50s Mercedes 300S. Carby clean?

Answer 3

Assuming the engine ignition timing was set properly and there's no reason to believe it has changed, I would nevertheless first verify the proper timing at idle using a timing light. Then I would start looking for a vacuum leak which is any source of air getting into the engine that's not going through the carburetor venturi. Improper timing and vacuum leaks can definitely cause a rough idle. You can temporarily block off the major vacuum hoses that lead to your power brake booster etc. to see if the rough idle evens out. Of course we're also assuming your basic tune-up items are in good shape. GM has a "top engine" cleaner product that removes engine carbon buildup (you dump some into the primary intake of the carburetor). Another assumption is that you meant the hot idle was rough. Other things affect the cold idle problems. Check that your Positive Crankcase Ventilation (PCV) emissions system is flowing properly. Besides checking the PCV valve itself, sometimes you have to remove the carburetor and clean out all the PCV passages that may have become blocked by carbon. Of course the carburetor itself can induce a rough (hot) idle if its idle circuits or adjustments need maintenance. You could buy a new spare carburetor ($500) and exchange it with yours to see if there's any performance improvement. Finally, we're assuming your engine is in good shape, since timing chain wear, valve problems and carbon build up can contribute to performance problems.

Answer 4

my civic was doin that, like it idles low den high den or something close to it - my bro was like it wasn't gettin enough oil but it drove fine, just idled funny but today my transmission gave out so i dont know if that was leading up to it or not

hope it helps

Answer 5

Sounds like the choke.

Answer 6

Maybe a small vacuum leak

Answer 7

start with a full tune up before you go spending money on this and that...you have a carb on that thing? clean it and look at the choke... Points??? clean them with a emory board...gently..

Answer 8

check spark plugs, wires, plugs, carburetor, fuel filter,