Idle is up and down?

[Fairlaniac]

1991 Ranger 2.9. I picked this up recently and doing some tune up and maintenance. The engine doesn't idle steady. It semi-idles at 1000 RPM or so and dips to 500 RPM or so about every second. So it's like saying vroom-vroom-vroom on one second intervals. Any idea? No codes showing up. IAC?

Thanks!

 

[509lifted]

fuel flow problem or maybe timing

 

[kimcrwbr1]

Check all your vacuum hoses did you replace the PCV and any cracked or hard hoses. Disconnect the battery and clean the throttle body around the butterfly, pull the idle air control and clean it with carb cleaner and pull the MAF sensor with rubbing alcohol. Connect the battery and run it around 20 minutes and see if it idles correct.

 

[Fairlaniac]

re:

Check all your vacuum hoses did you replace the PCV and any cracked or hard hoses. Disconnect the battery and clean the throttle body around the butterfly, pull the idle air control and clean it with carb cleaner and pull the MAF sensor with rubbing alcohol. Connect the battery and run it around 20 minutes and see if it idles correct.

I'll look over the items suggested. I actually did an intake gasket change over the weekend, coolant leak. It did the erratic idle prior to the change and I was hopeful some of the 'cleanup" would help. The PVC I cleaned out good with Berryman's. The butterfly on the TB got a good cleaning. It was funny how the intake looked underneath where the injectors come out. 3 ports had a huge amount of build up around the injector spray. they were completely shrouded. Anyhow, a good clean up of the intake and it's passages, just shiney aluminum, no black or brown anywhere.

If I just barely put my foot on the throttle and hold idle ay 1000 rpm it runs smooth. Take my foot off and up and down 500-1000 rpm it goes again? It seems as it it were a carburetor with an idel screw it would need just a quarter turn to smooth out? Just an analogy. I did nothing with the IAC.

Thanks,

 

[adsm08]

It may be the IAC. My B2 does this from time to time as well, and I have not been able to figure it out yet. I know it isn't the IAC on mine because I swapped it with a known good one and it still does it.

 

[Fairlaniac]

re:

What bugs me the most about it is the alternator dips below a chargable RPM. So if I'm driving at night time and at a traffice light the fluctuating RPM has the headlights going dim-bright-dim-bright...... The volt gauge needle fluctuates with the rpm drop.

 

[kimcrwbr1]

Change the PCV there is no way to properly clean it, put a new one in with plugs or oil changes.

 

[Fairlaniac]

re:

New PCV, set timing, took off IAC, looked like a recent replacement but still cleaned up the little bit of soot. So now my idle is just low. The surging is gone but at hot idle it runs about 500 rpm and it's not enough to keep the alternator spinning where it should. If it had an idle screw all would be fine

Thanks,

 

[zekew64]

Just my $.02, but...

The 2nd-gen Rangers, of which the '91 is one, does not have an IAC. It has an IATC (Inlet Air Temperature Control) valve, which is only for warmup--and it operates on vacuum.

Second, OP, you should have an idle screw next to the throttle cable you can use to set your idle speed. At least, on my '92 2.3L, that's what I have. However, I looked into my Haynes manual, and there was no mention of an IAC system in the 2nd-gen Ranger family. The only setting for idle speed control is if you don't have EFI (that is, if you have a carbed motor). And that was only until the '87-'88 year models.

 

[zekew64]

Just my $.02, but...

The 2nd-gen Rangers, of which the '91 is one, does not have an IAC. It has an IATC (Inlet Air Temperature Control) valve, which is only for warmup--and it operates on vacuum.

Second, OP, you should have an idle screw next to the throttle cable you can use to set your idle speed. At least, on my '92 2.3L, that's what I have. However, I looked into my Haynes manual, and there was no mention of an IAC system in the 2nd-gen Ranger family. The only setting for idle speed control is if you don't have EFI (that is, if you have a carbed motor). And that was only until the '87-'88 year models.