My car's had a rough idle for a while now. I purchased a temperature probe and after warming up at idle cylinder#1 (as close to the head as possible) was measuring ~220 F while the rest were all around 300-350. Could this be an indication of a problem? What should I look for? I have OVC wires and they look good(and that's one of the easier ones to follow), plus there is shielding near the header so I don't think that's the problem. Any ideas?

Thanks all,
-P.J

 

This problem has been plauging me for a while now and I finally have a lead(or so I think)- can anyone help??

 

Sounds like a leaky injector. Check fuel pressure after the engine is shut down to see how fast it drops. Do a leak down test also.

 

Fuel pressure is good, also had the injectors cleaned and flowed. I did have one slightly leaky injector but it wasn't that cylinder- car runs the same now.

Swapped plugs and wires with a new set and it didnt help. Any more ideas!?

 

Anyone, please!?

 

Welllllll, what is the condition of the car? Have you been racing it? Running nitrous? Supercharger? How many miles on it? But when in doubt, you can do a compression check to see if you have compression, the same, in all the cylinders. if there is a noticeable difference in the cylinders, you can do a bleed down test, and that will give you an idea whether it is rings or valves. By using an ohms meter, you can check your wires for resistance. If a wire has no resistance, then the wire is bad. Start with the little things, and start working your way up.

 

Car has about 85k, no nitrous or supercharging- stock except headers. All the small things(sensors, etc) have been replaced in hopes of fixing the problem. Wires are good because I swapped them with another set and had the same issue. I guess I'll have to get a compression test done- is that something I can do myself or will I have to take it in?

 

Did a compression test on the left bank(too hard to do on the right, and the cold cylinder is #1). Readings were
#1-180
#2-180
#3-180
#4-180 (me and a buddy did separate readings, he claims it was 200 on #4)

Replaced all the plugs while I had them out, replaced the TR55's with stock Delco plugs, no change in rough idle or the cold header.

I did notice that the #1 header is out on its own compared to the rest, I realize this would keep it slightly cooler, but I strongly doubt it would by 100 deg. Has anyone else with jet-hot/hooker longtubes taken readings?

I really need to find the cause for my rough idle, and was hoping the cold header would give me a clue to where it was- but the compression test pretty much threw me back to square one. Is there any way to check the injectors are getting the proper electronic signal?

 

The injector is getting pulse and there is definately spark at cylinder #1, I used testing equipment to verify this. However it is still noticeably colder and the funny part is when I disconnect the spark plug and injector connection the car idles exactly the same... Is this normal?

 

You may have a flat cam lobe. Pull the valve covers and see if there is a broken spring and all rockers are moving the same. Or a bent push rod. Or a rocker off of a valve.

 

I pulled the valve cover to give it a look and everything seemed tight and in order as far as rockers and springs, but that still leaves the cam and pushrods as possible culprits- is it going to make an oily mess if I run it with the cover off?

 

Put some shop towels over the pushrod end of the rockers. Yes it will make a mess,but there is no other quick way to tell.

 

I was thinking about pulling the pushrod first and inspecting it if it's not hard to do. If that's straight then I guess I will have to run it and if things aren't moving properly assume it's the cam.

Thanks for your help!

 

Can someone explain how to pull/reinstall the pushrod? I tried searching and got more confused if anything by all this talk about valve lash, preload, etc.

 

If you have a valvetrain problem, it would be unlikely that you don't hear the problem and it would also be unlikely that it would only be noticable at an idle (you didn't say that the motor runs rough at any rpm other than idle). But if you want to check the cam lobe(s), disconnect the opti-spark so the car won't start and crank the motor over with the valve cover off and compare the movement of the rockers to one another (doubtful you will see a difference). Pull the sparkplug for the cylnider in question, is it fouled??? Swap plugs and wires with another cylinder to verify there isn't a problem with either of those. Pull the cap and rotor and look for a burnt or worn terminal. Swap injectors from a different cylinder to verify it is not the injector. Not necessarily sure that the cylinder with the lower temp at idle is the culprit. The temp. difference between cylinders at an idle can vary several degrees. Do the cylinder temps become closer to one another when the motor is brought off idle? Oil pressure changed??? Have to had to add coolant to the radiator??? Does the rad. hold pressure??? Checked for vacuum leaks??? Throttle body/IAC clean??? The list can go on and on. Check some of these to try and narrow it down and post your findings, we will try and help!