Ocassional Rough Idle!! (Im Outta Ideas)

[GOBULLGO]

I have no clue what is causing a rough idle occasionally in my dohc sable with 190K when at a traffic light.(rpm does not budge engine just like "shutters") Doesn’t occur all the time. Today it was in the 20’S and very windy and it was WORSE. NO CHECK ENGINE LIGHT ON. (yes check engine light works) NO PROBLEMS DRIVING, DID A PROPANE TEST AND SPRAYED STARTING FLUID ALL ROUND THE INTAKE AREAS and no change in idle. SCAN TOOL shows no errors....

ANY IDEAS? This has been an issue for close to two months. Needless to say Im really starting to hate this car.

Last winter I changed the following:
Upper and lower intake manifold gaskets
Plugs, coil pack, and wires, (Bosch Wires and Plugs)
pcv, mas airflow, egr, and several vacume hoses (the common hoses that evetually fail)

In the past two months I have replaced
Motor mounts, fuel filter and air filter. Ironically the issue occurred after I replace the fuel filter and air filter.
@ idle

LTFT B1 6.3 Long Term Fuel Trim-Bank 1
LTFT B2 7.0 Long Term Fuel Trim-Bank 2


@ 50mph

LTFT B1 -2.1 Long Term Fuel Trim-Bank 1
LTFT B2 -2.3 Long Term Fuel Trim-Bank 2

IM OUTTA IDEAS!!!!

[Jeff K]

With the higher positive LTFT ad idle and the low negative trims at 50 mph, I am guessing a small vac leak the effects both banks. Did you change the PCV hose or PCV valve when you checked for vac leaks?

Reading your post again..... BOSCH PLUGS????? Ford engines do not like Bosch plugs!!!! Put in the correct Motorcraft or equivalent Autolite plugs and see if the problem goes away.

[GOBULLGO]

Thank you Jeff.

I will get a cigar and try a smoke test tomorrow.
If that does not show indication of a leak then I will replace the plugs.

PCV Valve replaced Dec 2011 along with the vacume hose connected to the PCV Valve

[machineop]

I know the feeling I have an '03 windstar that does the same thing. Did you clean your IAC valve? I cleaned mine with some valevoline throttle body cleaner it helped a little but still not satisfied. I think the first warm day i get i'll take the throttle rubber apart and give it a good spray down. Good luck solving your problem!

[wi11ie]

Fling those Bosch plugs in the trash.. Motorcraft or Autolite Double Platinums will do the trick..

[behlinla]

+2 on the Bosch plugs. Take them out. They work fine for like 15k then you start having rough idle problems.

Fuel trims are pretty good. If the oxygen sensors are original you should replace them (the two upstream sensors).

[GOBULLGO]

Thank you all for your help. I changed the plugs to autolite (not sure if it was the Bosch Plugs or the fact that several plugs were loose). I did not change the O2 sensor that sensor near the firewall doesn’t look easy to change so i didn’t mess with it. I will follow-up in a week but hopefully the issue is resolved.

On a side note what is the easiest way of tackling the O2 senor near the firewall?

Also I changed the IM upper and lower even though they only had 30K miles on them but they did have some oil build up. What is oil buildup on the upper and lower manifold gaskets indicative of?

[behlinla]

Firewall-side O2 sensors can be tricky. You might have to take some things off (like the cowl) to get better access. Sometimes you have to get at it from below.

There will always be some oil in the intake with a PCV system, but if you think it's excessive I would change your PCV valve. Also inspect the PCV hose because they commonly crack and leak. If you are still getting a lot of oil it means you have blow-by.

[pawpaw]

Originally Posted by GOBULLGO

Thank you all for your help. I changed the plugs to autolite (not sure if it was the Bosch Plugs or the fact that several plugs were loose). I did not change the O2 sensor that sensor near the firewall doesn’t look easy to change so i didn’t mess with it. I will follow-up in a week but hopefully the issue is resolved.

On a side note what is the easiest way of tackling the O2 senor near the firewall?

Also I changed the IM upper and lower even though they only had 30K miles on them but they did have some oil build up. What is oil buildup on the upper and lower manifold gaskets indicative of?

When changing my Gen-2 O2 sensors, I made use of Advance Auto's "Loan-A-Tool" for a refundable deposit program, to check out their O2 sensor socket wrench set. It had a short offset socket that made all the difference in getting to & making the removal of the firewall O2 sensor a breeze from below.

[GOBULLGO]

Seems like changing the Bosch plugs to autolite resolved the issue. Several plugs were noticeably loose, so the new autolite’s got torqued to 15 ft lbs.