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quickcar
quickcar, ASE Certified Technician
Category: Dodge
Satisfied Customers: 1695
Experience:  10+ years chrysler
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1991 Dodge Stealth: RT..replacement it idles at 2500 rpm when its cold

Customer Question

Hello Chris, 1991 Dodge Stealth RT DOHC. I had the engine replace last year with a Japanese take out. Ever since that replacement it idles at 2500 RPM when its cold. It takes about 15 minutes to settle down. When its warm it idles at about 800 RPM. Its smooth and runs fine down the highway. The idle set screw on the throttle cable is backed completely out and the idle jet on the top (don't know what its called) is screwed all the way in (slowest idle). Neither were set this way with the original engine. The swapout mechanic is experienced and worked on it several times in an attempt to find something connected incorrectly. No luck. We both eventually gave up... but it bugs me because I know its not right. Any thoughts? Sure appreciate your feedback. Thanks Martin
Submitted: 5 years ago.
Category: Dodge
Expert:  quickcar replied 5 years ago.
hello, id like to try and assist you, if your stealth has a plastic intake manifold it may be cracked somewhere, it sounds to me like you have a vacuum leak that seals itself up as the engine warms up, to find it use brake cleaner or water and spray around the intake manifold with the engine running cold and see if the idle changes or the engine stumbles f it does then you have a vacuum leak in that area.
Customer: replied 5 years ago.

Thank you. The intake manifold is not plastic... but I like your idea and will spray around the hoses and manifold.. I'll let you know.

Expert:  quickcar replied 5 years ago.

no problem, i had a dodge neon do the exact same thing as your stealth is doing and the manifold, which happened to be plastic was cracked.

 

Customer: replied 5 years ago.
Ok.. I started the Stealth and spayed it with engine degreaser... No change in rpm.. I thought perhaps that wasn't flamable enough so I armed myself with a fire extinguisher and sprayed starting fluide at the intake gasket and all the hoses... No luck. After about 15 minutes it settled down to a normal idle. At that time I could still rest my hand on the intake manifold.... warm but not hot to the touch.. Good thought, but I don't think that's the answer.. In the old days with carburated engines there was a spring that took heat off the manifold and adjusted the choke as the engine warmed. It seems like there has to be a thermal sensor somewhere on this engine that performs a similar function??? Any ideas?
Expert:  quickcar replied 5 years ago.
a couple other things to check would be the engine coolant temp sensor, and the intake air control valve.
Customer: replied 5 years ago.

Another thing to consider... yesterday I failed emissions big time. Now, the idle problem has been going on for more than a year. In other words, last year I passed emissions with flying colors while the idle problem was still occuring. This year, High Speed HC registered 827 and idle HC was 415. Not sure these are related.. but if we're talking about potential air flow sensor... maybe that's related?? Where is the Air flow sensor?

Expert:  quickcar replied 5 years ago.
the idle air control valve is located on the throttle body.
Customer: replied 5 years ago.
I've been reading the service manual.. troubleshooting section. At one point, I wound up on the task to remove possible deposits from the "throttle valve." Is that the same thing you're referring to.. If so, I'll execute that procedure tomorrow night...
Expert:  quickcar replied 5 years ago.
yes i believe that is refer to the same thing.
Customer: replied 5 years ago.
I followed the procedure to clean the throttle valve. This involves removing the air intake.. then you're supposed to plug the bypass. There wasn't a diagram so I don' tknow what they were referring too. I also can't see the throttle valve... The only thing I could see were two small openings on the bottom of the throat.. and it looks like perhaps a valve under that... I couldn't really tell for sure. I spayed cleaner into that area. When I started the cold engine with the intake disconnected the engine idled at 1500... just about what I would expect.. I put the intake hose over the throttle body air input and it raced up... to 2500... Removal of that intake shouldn't affect the vacuums generated by the intake manifold.. there is only one small secondary vacuum hose connected off the big air intake hose and it goes to the bottom of the intake ... seems like that's where the PCV valve would be... I don't know if that's the case or not... I'll start the cold engine tomorrow and let you know what happens.
Expert:  quickcar replied 5 years ago.
let me know
Customer: replied 5 years ago.

Nope. Two days ... same results. No good. I'm at a lose.

Expert:  quickcar replied 5 years ago.

does it still idle normal with the air duct off?

 

Customer: replied 5 years ago.

Yes. In fact, now I've determined that it will idle normal if I put the air duct back on and unplug the air flow sensor connector. I took that box out, replaced the air filter and used some air sensor cleaner on the gridwork... it looked very clean when I started and still did when I reinstalled. It didn't help. As soon as I plug it in, the engine idle increases again. It must be sending signal because it definately doesn't run right with it off.... it idles ok but stumbles and misses when you rev it up... also check engine comes on .. Checked on a replacement just for the heck of it.. 330 bucks from checker.. I wouldn't want to do that unless I could test this one and determine it was bad for sure.. Any ideas?

 

Expert:  quickcar replied 5 years ago.
well thats actually what i was going to to suggest, i believe that is the mass air flow sensor, and while i agree with you that 330 bucks is an expensive guess, i believe that is the culprit since that is the only thing you were able to do to get it to change.you could try turning the key off on off on off on and see if the check engine light flashes any codes they usually are 2 digit codes the light will flash a certain number of times for the first digit then pause and flash a certain number of time for the second digit.
Customer: replied 5 years ago.
Given that it gets better when its warmed up.. is there an air temperature sensor in the mass air flow sensor too? Or is that somewhere else. It seems like its more of a temperature thing than an air flow thing.
Expert:  quickcar replied 5 years ago.
on those particular cars i believe the temp sensor is part of the mass airflow sensor.
Customer: replied 5 years ago.
I broke down and took it in... they felt the mass air flow sensor was a good bet and replaced it.. That didn't do it.. they replaced the evaporative fuel canister .. and the throttle servo.. It passed emissions with flying colors and the idle issue is resolved.
Expert:  quickcar replied 5 years ago.
hello im glad its finally fix then, these things can be very difficult to come up with sometimes.
Customer: replied 5 years ago.
I'll say. Thanks for your efforts...

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