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That rough idle with ac on dan replaced but.

 
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Old 01 Nov 2017, 10:50 am
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Location: South Carolina
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Default That rough idle with ac on dan replaced but.

Hello all,

I had that rough idle while stopped with the ac on..the fan was replaced and now it is a mild rough idle but it went down from a 10 of 10 to about a 3 of 10 roughness. The dealership did the install and before I call them I would appreciate some insight of possibilities.

Thank you,
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Old 01 Nov 2017, 11:03 am
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Default Re: That rough idle with ac on dan replaced but.

When you turn the A/C on, the compressor is now loading the engine more. That would account for the roughness. Many cars compensate by increasing the idle speed, but at a stoplight with your foot on the brakes and an automatic transmission, the faster idling engine is fighting the transmission and the brakes.

As an experiment at a long traffic signal, put the car in neutral. You'll notice the RPM's go up on the tachometer and I'll be a smoothing of the engine vibration. Don't forget to shift it back into drive

The important thing is that the fan is now working and the A/C compressor isn't overheating and really loading down the engine. You can also check the operation of the fan by lifting the hood with the A/C off. Then turn the A/C on and look at the engine compartment again. It should sound like a tornado in there with air blowing all around. That's the radiator fan at high speed.
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Old 01 Nov 2017, 11:50 am
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Default Re: That rough idle with ac on dan replaced but.

Quote:
Originally Posted by squarebeer View Post
Hello all,

I had that rough idle while stopped with the ac on..the fan was replaced and now it is a mild rough idle but it went down from a 10 of 10 to about a 3 of 10 roughness. The dealership did the install and before I call them I would appreciate some insight of possibilities.

Thank you,
:
I would suggest checking your motor mounts.

The link below will help you determine if you need to check your motor mounts.
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Old 01 Nov 2017, 01:18 pm
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Default Re: That rough idle with ac on dan replaced but.

Quote:
Originally Posted by squarebeer View Post
Hello all,

I had that rough idle while stopped with the ac on..the fan was replaced and now it is a mild rough idle but it went down from a 10 of 10 to about a 3 of 10 roughness. The dealership did the install and before I call them I would appreciate some insight of possibilities.

Thank you,
:
Okay, you have a 2009 PT, right? Also, did the engine overheat when the fan was out? And has the check engine light come on?

In addition to what rsrocket1 said, you may want to consider the last time you changed the plugs and wires. Rough idle in a PT usually comes down to bad wires/plugs, vacuum leaks, bad idle air valve or low compression on one or more cylinders. There's other causes too but these seem to be the most common.
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Old 01 Nov 2017, 01:19 pm
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Default Re: That rough idle with ac on dan replaced but.

I've had a rough idle on my PT since i bought it new. Had it in for service a few times because the car would actually stall every now and then, when going into drive or reverse. They changed the plugs at one visit, the wires on another (covered under warranty). They never could fix the problem and I've been living with it for all 85K miles. It's just become an annoying quirk that i've come to live with. I've been through numerous threads on here over the same complaint and have yet to hear anyone come back with a fix. Good luck on your endevor, and please keep us posted if you find a resolution to your problem.
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Old 01 Nov 2017, 01:28 pm
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Default Re: That rough idle with ac on dan replaced but.

Quote:
Originally Posted by Grasshopper77 View Post
I've had a rough idle on my PT since i bought it new. Had it in for service a few times because the car would actually stall every now and then, when going into drive or reverse. They changed the plugs at one visit, the wires on another (covered under warranty). They never could fix the problem and I've been living with it for all 85K miles. It's just become an annoying quirk that i've come to live with. I've been through numerous threads on here over the same complaint and have yet to hear anyone come back with a fix. Good luck on your endevor, and please keep us posted if you find a resolution to your problem.
Hey Grasshopper,

Did they ever do a compression test on your engine? A leaking valve from the factory might do this. A weak injector from the factory might do the same.

It's hard to know what diagnostics the dealership has done, but if assuming the dealership did most of the obvious stuff already, I might do my own compression test and I'd check the manifold vacuum from idle to 3000 RPM. And I might even trade out the injectors with a set from a salvage PT. The compression and vacuum tests cost nothing and a set of salvage injectors and new o-rings all together is about half the cost of one hour of shop time for more diagnostics. Just some ideas to think about. It's a four cylinder so idle is never the best, but a PT engine should be relatively smooth at idle.
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Old 01 Nov 2017, 01:37 pm
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Default Re: That rough idle with ac on dan replaced but.

Quote:
Originally Posted by squarebeer View Post
Hello all,

I had that rough idle while stopped with the ac on..the fan was replaced and now it is a mild rough idle but it went down from a 10 of 10 to about a 3 of 10 roughness. The dealership did the install and before I call them I would appreciate some insight of possibilities.

Thank you,
:
Did the dealership indicate why the Pt Cruiser still has the mild rough idle? Always get as much information as you can when you are diagnosing a problem so you are not wasting funds on plugs and wires, etc. as previously posted in this thread. Throwing parts at it is not the best way.
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Old 01 Nov 2017, 01:38 pm
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Default Re: That rough idle with ac on dan replaced but.

Quote:
Originally Posted by Handy_Cruiser View Post
Hey Grasshopper,

Did they ever do a compression test on your engine? A leaking valve from the factory might do this. A weak injector from the factory might do the same.

It's hard to know what diagnostics the dealership has done, but if assuming the dealership did most of the obvious stuff already, I might do my own compression test and I'd check the manifold vacuum from idle to 3000 RPM. And I might even trade out the injectors with a set from a salvage PT. The compression and vacuum tests cost nothing and a set of salvage injectors and new o-rings all together is about half the cost of one hour of shop time for more diagnostics. Just some ideas to think about. It's a four cylinder so idle is never the best, but a PT engine should be relatively smooth at idle.
You are hijacking this thread. If you want to help another member I would recommend you do it on a new thread.
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Old 01 Nov 2017, 02:37 pm
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Default Re: That rough idle with ac on dan replaced but.

I appriciate the help, but after 9 years and 95K miles, i don't plan on making anymore efforts chasing it down. Especially when my wife is shopping for a new car. Its been in and out of the dealer mutiple times under warranty to try and solve the problem (Sensors, plugs, wires, seals, all changed at different visits and nothing worked. The first time I took it in, the car had less than 100 miles on it.The last time I took it in was just after my 3/36K experied. I was thinking maybe they would get to the root of the problem after the warranty expired and they were on my dime, but their master mechanic wrote it off as "thats just how the PT's idle". After reading a number of threads on the topic, i don't ever recall anyone coming up with a resolution for their problem. I just learned to live with it and thought i'd share my exp. with OP. Not sure how bad their idle is, but if its more an annoyance, they may be better off learning to live with it, like i have, than running down the rabbit hole looking for a silver-bullet fix.
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Old 01 Nov 2017, 02:47 pm
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Default Re: That rough idle with ac on dan replaced but.

Like handy mentioned, a bad or dirty IAC could cause a bad idle. Cleaning or replacing didn't resolve mine, but it's probably one of the easiest things you could try to resolve your issue. Here's a link for ref.

Rough Idle-Replacing the IAC Idle Air Controller
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