StealthElephant

My engine has been acting kinda funny...it revs kinda low sometimes....in gear when fully warmed up it will idle like 750, and drop to 600 and go back up to 750, in a way that the car rocks back and forth. Sometimes in park when fully warmed up it will hold 900 smoothly, and sometimes it will sit at 750 and rock up and down. Its not a slight change in engine speed, it rocks the car.

90rocz

A/C pump kickin in and out? Like when you run the defroster?
Vacuum leak?

dj haf

check your plugs. i know that used to happen to me a lot when i was at idle after my car warmed up... changed the plugs one day and it all went away and so did a few other problems i had... get yourself some GOOD plugs, i like rapid fires they fixed everything right up.

doug791

okay with a miss you will quite often get what feels like a drive train vibe because it takes the engine out of balance. Also with a miss is you stand right by the exhaust and listen reeeally closely itll sound like, lub lub LUB lub lub lub lub LUB lub, youll hear a noticeable noise of the cylinder thats not fireing. If it sounds nice and steady its probably not a miss.

Questions does it do this randomly? or once the car is warm for a while do these problems go away? It sounds like a less severe case of when i had my coolant temp sensor go bad on me. Check to see if you have any codes because it wouldnt surprise me if you had a sensor going out on you.

StealthElephant

Doug: My coolant gauge doesn't even work, I'm guessing my sensor doens't either.

The engine is acting wierd to begin with. I set the idle in park @ 850RPM, and once fully warmed up and in gear it idles irradically around 600 like I mentioned. It keeps reving up and down from 500-750, which is a pretty big jump. It's not a consistent thing it will do it 75% of the time, but its irradic. As mentioned, its not a "lub lub LUB lub lub lub lub LUB lub" but it will pace for like 6 seconds, smooth itself out for 2 seconds, then start pacing up and down again for a few seconds, then smooth out again. If I hold the gas and hold the RPM at 800-1000 it will simply hold that RPM smoothly. I dunno my buddy has the exact same 350 build as me, same cam, same ignition/distrib setup. Only difference is hes running 462 fuelie heads and 10:1 CR as opposed to my 10.7:1. His engine idles smooth as hell.

It shouldn't be a vaccum leak, because when the engine was first built we had trouble and we took the intake off and regasketed it.

I pulled the #1 plug out when I put my distributor back in, and it was in perfect shape (though it had like 200 miles on it). Im runing RTLS42s. The engine is happy, I had it up to like 4000 the other night and it didn't have any problems. Just something wierd at idle.

mechanicZ

i'd check the plugs, but sounds more like a vaccum leak 2 me

doug791

check for codes, and you really do need that coolant temp sensor. When i bought my car it was running perfect and coincidentally as soon as it gets home it starts running like crap on a stick. It would start and ran rich as a pig, idle was somewhat erratic, car would bog and stall every now and then. Checked codes, said the sensor was bad, replaced it, car ran perfect.

You didnt answer if the problem goes away once the car has been running oh lets say 10-15 minutes. This is important because if its a sensor issue there are a bunch of sensors that work until the O2 sensor warms up enough then that mainly takes over (not completly mind you).

Once you check for codes you then have to go the guess and check route. Most simple thing to start with is the 4 simple rules of an engine, fuel, spark, air, and compression. Try to isolate each one and make sure youre getting enough of it.

StealthElephant

It does it all the time, fully warmed up etc etc. My TPI is pulled, I put a non-computer controlled carbed 350 in.

doug791

ahh that info was kind of important and im apparently too stupid to have just looked in your sig ..... hmmm i know a lot less about carbed motors then efi so this is where i take a step to the side.