420A Rough Idle & CEL

[1BadRS]

So for the past month I have noticed the car doesn't want to hold a constant idle and then every now and then the CEL will come on. It hasn't got to the point where the car wants to stall at a light but when ithe rpms drop lower than normal it starts shaking my steering wheel. So this weekend I decided to check out the throttle body and sure enough it was just covered in carbon. Got out my retired tooth brush, some carb cleaner, and towels and cleaned it up the best I could with the throttle body still attached. All I can say is wow you never think stuff like this makes a noticable difference but it is like night and day now. Not only do I not have a CEL and my idle is solid as a rock, but it actually seems to have better pickup.

Anyway I just thought I would share this with anybody that has similar symptoms. The best fixes are the ones that don't cost anything

 

[Locke]

Now imagine how much of that crud is still in there that you couldn't reach. You may notice even more of a difference if you remove the TB and IAC and clean them more thoroughly.

Free fixes are great. I hope you don't have any more problems with the vehicle.

 

[Styl]

I'll definitely have to try this on my '90 GS. I was in the process of putting a fuel filter on it the other day and took my intake hose loose from the TB to reach the filter better, and noticed that the inside of the hose was oily as all hell, and the TB wasn't in much better shape. I've been having some rough idle probs with the car for a while now, and even though the A/T tranny is bad in it, I've been working on it as a project car. I've already done the spark plugs and wires (NGK), fuel filter and new air filter, so I'll definitely be trying this next.

 

[murray1]

I didn't want to start a thread for this but I noticed that I couldn't post in the non turbo FAQ and was just going to post in the CEL one saying that you can also use keydance which comes in really handy, I was going to provide link to the table on 2gnt and say that with a little bit of searching on here or 2gnt you can usually diagnose the problem via keydance.

 

[VelocitàPaola]

Now imagine how much of that crud is still in there that you couldn't reach.

That's what Seafoam is for.

I recommend that stuff for anyone. I've used it on every used-car that's passed through my care.

 

[mopar_21]

I had a similar issue where the cel would disappear as soon as it left idle and return upon idle. I took my throttle body off to clean and inspect the ISC to discover the ISC was rusted shut. I just bought my talon a few weeks ago fixing it up, and before that it sat for five years.