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Technoid · 08-27-2022, 09:15 AM

I have a Pace Arrow 1999 with F53 chassis. I have an engine problem. The RPM will hunt up and down about 200 RPM. I don't know what is causing this. It's fine on highway speeds. But as soon as you stop and idle or stop with no load and run up the rpms it will start it's 200 RPM hunt. What should be checked? The A/C is off during this test and not on defrost.

Tha_Rooster · 08-27-2022, 09:27 AM

Quote:

Originally Posted by Technoid

I have a Pace Arrow 1999 with F53 chassis. I have an engine problem. The RPM will hunt up and down about 200 RPM. I don't know what is causing this. It's fine on highway speeds. But as soon as you stop and idle or stop with no load and run up the rpms it will start it's 200 RPM hunt. What should be checked? The A/C is off during this test and not on defrost.

Dirty injectors?

sandwip · 08-27-2022, 07:16 PM

The first thing I would check is your EGR Valve, which I believe you have on a '99. Check the valve for vacuum and check your hoses.

code2e · 08-27-2022, 07:36 PM

I would clean your throttle body. This is the cast aluminum housing at the top of the intake manifold. Has the air intake hoses coming to it from the air filter.

The butterfly throttle plates get build up around them in the closed position. The buildup can keep the plates from closing completely. This can make the idle air control "hunt" trying to control idle speed.

Get an aerosol can of throttle body cleaner from any parts store or Amazon. Remove the air intake hoses and hold to the side. Run the engine at idle and spray the cleaner lightly into the engine. Not so much to make it die at first. After 10 seconds of light spray, give it a full burst for a second. It will die. Let it sit 10 minutes. Start and run at fast idle 10 seconds. Shut off and have a look. You want bores and plates clean. Repeat only if needed. Usually once is enough. Reattach air intake hose. Short drive and should idle better.

donr103 · 08-27-2022, 07:48 PM

Code2e is right on the mark.. but in my opinion.. I use old toothbrush and with engine off.. hold open throttle butterfly and use cleaner and toothbrush to clean.. and yes.. let sit 30mins and as long as good and clean.. reassemble and try.. I would also go ahead and pull IAC. Valve and clean that.. and clean passages to IAC valve on throttle body.. too.. you are right there.. you will need to replace gasket or use rtv.. then give that a try.. if not.. clean egr..
Good luck and keep us posted

code2e · 08-27-2022, 08:56 PM

Quote:

Originally Posted by donr103

Code2e is right on the mark.. but in my opinion.. I use old toothbrush and with engine off.. hold open throttle butterfly and use cleaner and toothbrush to clean.. and yes.. let sit 30mins and as long as good and clean.. reassemble and try.. I would also go ahead and pull IAC. Valve and clean that.. and clean passages to IAC valve on throttle body.. too.. you are right there.. you will need to replace gasket or use rtv.. then give that a try.. if not.. clean egr..
Good luck and keep us posted

Using a toothbrush would be ok as long as a very soft bristle. Scratches are bad if they cross the seal line where the blades seat.

There are side benefits to the running spray I advocated. At idle, the spray passes thru the idle air control and soaks it when the engine is killed by full spray. Also, the oxygen sensors get a little bath as well.