Hi all,

I have a 93 2dr Ranger with 3.0 V6 engine. The truck developed an unstable idle problem for the last 4 months. When the weather is cold or when I start the engine in the morning, the engine cycle from 1700 to 500 rpm until the engine warms up.

I removed the IAC valve this morning. The IAC port has a lot of oil and carbon build up. Cleaned it out with the carburator spray. Now the engine warms up with a consisten 1700rpm and slowly reduces to 800 rpm with steady idle.

Just to make sure everthing is clean up, I cleaned out the manifold intake hose. I found out it has some oil blowback from the valve cover. Maybe this is the cause of the IAC carbon build up. Anyway the everything seems to be working normal again. The truck is up for bi-annual smog check so I changed the plugs and put in a new distributor. The whole operation takes just over two hours. Spark plug removal took the longest, especially with the #3 plug, the rearmost plug on passenger side.

I like to thank all the folks that posted here over the years. There a wealth of information in here if anyone care to search for.

BTW, I bought this Ranger new in 1993. It has +252k miles and still running fine so far. The hefty power, if any, is no longer there and the manual transmission feels like it has a million miles on it. But it's still good for the weekend Home Depot project hauler and daily driving. Who says American car company can't build a reliable vehicle.

 

I did it. Oil and dirt comes there from cranckase vent. system. Mixed with dust that may go throught air filter this mix makes valve stuck

 

Yes that's the terminology I was looking for. The vent port on the air intake hose has a slight oil coating. Not much but enough to slowly build up over the 16+ years of driving. I drive mostly in the city so it's not too dusty. I can imaging someone normally drive on dirt road having this problem much sooner

 

PCV is one of the oldest emmision requruments. some of drivers who's engines smoke like an old steam ship use a pice of garden hose and let carter gas out freely, but this is not legal... Cop can see smoke from under a truck. ))

 

Luckily the truck is not smoking yet. At least not visible. When pulling the plugs today, #1 cylinder is showing sign of oil, the electrode is slighly dark with carbon. Not too much but it indicates the rings are worn which allows some oil to blow past in the down strokes. If I check for compression, it should show slightly below the specs. The other plugs still shows good heat sign. Not too bad.

When I checked for smog two years ago, the O2 and CO are in the middle of specs. The NO level is borderline. This mean there is some carbon in the cylinder and possibly in the valves too. I need to get some injector cleaner which will help clean out most of the gunk.

 

Welcome to FTE.

Good to hear you got your cold idle problem fixed, but be aware that cleaning the IAC might not last, it didn't for me.

If you've never changed the PCV valve, it's likely worn out & may be parially responsible for the blow by that clogged up the IAC.

If you want to decarbon the engine wthout fouling up the new plugs, run most of the present tank of gas out, add a 20oz bottle of Techron Concentrate Plus at the pump before filling up with Chevron, Texaco, or CalTex gas, as they already have Techron in them, this will raise the treat rate 10X above pump gas & may do the decarb in one treatment.

Then do some spirited accelerations with rpm's above 3500, for a mile or so, or take it for a 20 mile highway drive during the treated tank & run most of the treated tank out before refilling. If you think it's carboned up bad, do a second treatment.

If you think the ring lands are carboned up & the rings are sticking, maybe consider an Auto-Rx treatment, to free up the rings & tidy up any engine deposits. It's an ester based lube thats added to the crankcase & run for a specified time to slowly soften & loosen deposits.
I've not had to use it, but haven't read of any bad results on the net & some folks using it have reported reduced oil consumption & plug oil fouling.
You can check it out here to see if it's for you. Auto-Rx Cleans Internal Engine Transmission Motorcycle Power Steering Differential Diesels, Stop Leaky Seals, Oil Burning, Increase MPG

 

Thanks for the tips on the decarbon treatment. The PCV is changed every 2 years before the smog check is due.