DSDRPM Question

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09Ranger
Posts: 20
Joined: Sat Aug 23, 2014 7:46 pm
Vehicle: Ranger, 2.3 Duatec, 2009

DSDRPM Question

Post by 09Ranger » Sun Aug 31, 2014 6:26 pm

Is the Desired Idle RPM a constant or variable?

That is, does it's value come from a table in the computer or is it a learned value that can be influenced by the various sensors?

I ask because my service manual lists my idle speed as 750 rpm. The computer has a DSDRPM of 848. There's no arguing with the computer so it idles at, or close to, 848.

If I unplug my IAC, the idle falls to 750 and I like that a lot better. It feels much more relaxed and I was wondering if there is any way to get the idle to that lower RPM.

Thanks,
Walt

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Posts: 2610
Joined: Fri Jun 13, 2014 2:21 am

Re: DSDRPM Question

Post by FORScan » Mon Sep 01, 2014 11:31 am

Desired RPM is not a constant, it is value PCM tries to reach. In your case PCM tries to set 848 RPM and, according to your post, successfully. The way it makes it depends on engine, on Duratec it is usually managed through IAC.

Good questions is why PCM tries to set 848 RPM. It means PCM considers this speed optimal. It may be normal on a cold engine. If engine is warm (engine temperature is 65 degrees of Celsius and higher), check data from sensors (ECT, MAF, MAP, IAT etc). If they are ok, it may be some mailfunction like intake vacuum leak. By the way, increased idle RPM is quite popular problem on different models.

09Ranger
Posts: 20
Joined: Sat Aug 23, 2014 7:46 pm
Vehicle: Ranger, 2.3 Duatec, 2009

Re: DSDRPM Question

Post by 09Ranger » Tue Sep 02, 2014 5:23 pm

Didn't really want to hear that. Vacuum leaks are notoriously difficult to find.

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