420A Idle RPM at 1500 to 2000

[Gothic_Tomgirl]

I have a 99 eclipse rs 2.0 n/t 5 speed I had a check engine P0171 light and replace all the the parts oxygen sensor, fuel injectors, vacuum hoses, spark plugs, wires and ignition coils.
I reset the ECU drove it for 30 miles and rpms still idle at 1500 to 2000... There no check engine light car is fine just high rpm. Also I let to car idle for another 10 minutes the reserve reservoir started to bubble and pushing ou the coolant..
What can the problem be now...

 

[steve]

Two things I check off the bat given what you've done so far are make sure your throttle cable isn't tight and holding the throttle butterfly open and making sure you don't have any vacuum leaks.

 

[Gothic_Tomgirl]

I checked the throttle cable it's good and there's no vacuum leaks either. Maybe it needs a new/used ECU?

 

[JeffGS-T97]

Your throttle body gasket may be bad. I had that same issue back in 2006 on my 420a. The gasket is right after the flap and will act as a huge vaccum leak and the engine revs higher at idle to achieve optimal vac. At idle spray a little carbon cleaner at the TB gasket area if it revs up the gasket is toast and will need a new one.

 

[Gothic_Tomgirl]

I found the problem... The throttle body gasket was still good but, did put a new one just in case but, the TB had alot of sludge built up. I cleaned it up and now it idles around 900 rpm now. Took it for a 20 mile drive and works like a charm...

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[JeffGS-T97]

Good job!

 

[BLACK'98DSM]

The combination of a bad PCV valve and the EGR causes that sludge. Before I installed my aftermarket throttle body, I deleted the EGR and installed a new OEM PCV valve. Also did some major cleaning imif the intake manifold.

 

[steve]

That's just gross.

 

[BLACK'98DSM]

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PCV valve dumps oil in there, then the EGR bakes it... I bet my runners are still as shiny as they were when I polished them without all that pollution.