Rich rough idle on a 87 with 2.5 engine and 5 speed.

I suspect this car sat for a couple of years or more and maybe everything is varnished up. I have replaced fuel pump, plugs, wires and ignition module. There is super nice blue spark at each plug.

Other than the engine running erratic, it will somewhat run good, but when it does it idling at 1800 RPM, (maybe a bad IACV?) no vacuum leaks, but when it decides to idle down it slobbers and rolling black exhaust and usually dies, The injector pattern looks really erratic as well, not a smooth funnel pattern like it should be.

Oh yeah no codes are turning on the Check engine light. I am surprised with the rich running, the code for the O2 sensor doesn't come up.

I'm thinking of taking the throttle body apart and cleaning it out and put in a kit, with a new pressure valve and maybe a new injector too.

Any thoughts here?

Many thanks,

John

Check the routing of your vacuum lines. In particular look at the one going to the MAP sensor. The MAP sensor is the #1 device the ECM uses to decide how much fuel to inject. No vacuum line to the MAP and the ECM thinks you are at wide open throttle.

Check your CTS. If the ECM thinks the engine is cold it will up the idle and it will run the engine rich. You can measure the resistance of the CTS or just replace it. You can also as a test stick a 150 ohm resistor into the CTS connector and see what that does to the idle. The 150 ohm resistor will tell the ECM that the engine is at 220 degrees. 1/4 or 1/2 watt works fine. Radio Shack $0.99

Most likely not an IAC - Why? No IAC code from the ECM. Also if the ECM has the idle faster when cold and slower when warm you know the IAC is actually working.

If the vacuum lines look ok try electrically unplugging the MAP. If that makes it run better and you do have vacuum at the MAP then replace your MAP

If unplugging the MAP doesn't make it run better try unplugging the O2 sensor. If that improves the idle then replace the o2 sensor. Note the ECM doesn't use the O2 sensor until the engine warms up. So if this condition is happening right from the start at a cold start it can't be the o2 sensor.





Note if you do decide to take off the throttle body. If you put the gasket on upside down on the throttle body you will block the IAC passage and the engine won't idle by itself. It might be the replacement gasket doesn't have an IAC hole in it also. Others have had that problem.

[This message has been edited by phonedawgz (edited 03-17-2011).]

Thanks phonedawgz, this will give me some place to start. About all I I know right now is, it's running terrible!

John

What does the spary out of the injector look like. Should be a nice cone spray and not drippy.

Any exhaust leaks or cracks in the exhaust. A leak in the wrong place can suck in air and fool the O2 sensor.

Phonedawgz,

Well the ECM coolant sensor must have been the culprit, I picked up a new one and decided what the heck for 20 bucks, it was worth a try. I installed it and it runs almost perfect.

There is a ever so slight hesitation when idling, it might come out of that when I take it for a long drive.

Dodgeruuner,

I do have a real small exhaust leak right at the manifold flange, I noticed that one of the exhaust bolts is broken off, so that most likely means the head is coming off

Thanks for the help guys, you are surpurb...!!!!!!

John

Cool Cool Cool

quote Originally posted by John N: I do have a real small exhaust leak right at the manifold flange, I noticed that one of the exhaust bolts is broken off, so that most likely means the head is coming off

exhaust leak there can cause problem... Any leak upstream of O2 sensor messes with fuel mix and no error code in ECM.

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