Irratic idle

[kody_lawrence]

I have a 99 ranger 4x4 w/ the 4.0l. A few weeks ago my trucks check engine light came on. At start up the truck will start and rev up to 1500 rpm and then will drop to about 200 rpm and then right back up to 1500 rpm, then will idle fine for a minute or two and then up and down up and down.

I took it to autozone and had them hook up their code tester to it and all it said was that it was running lean, which I imagine could be almost anything. Any thoughts?

 

[smokey]

Lean codes can mean a number of things are not right.
Check for vacuum leaks around the hose ,intake and brake booster. then go from there by getting the actual code number and post them up and some one should be able to point you in the right direction.

 

[97ranger4x4]

Yeh, usually two common codes are P0171 & 0174 which are bank 1 &2 lean, respectfully.

I would suggest what Smokey said and check for leaks in and around your intake. Also how has your truck been kept up maintence wise? New Plugs, wires, fuel filter, clean air filter, etc.? There are many sensors on our trucks that if dirty can make it a REAL PITA to figure out. Before you replace anything, inless its basic maintence and needs to be replaced, try and test each part. Purchasing good tools now will save you lots of money down the road with mechanics. A good volt/ohm meter is crucial for checking sensors. But others on her can give reccomendations. I dont understand it that well...

 

[kody_lawrence]

Yes the codes were 171 & 174. I just replaced the fuel filter and air filter. The air filter was not that old, but when I inspected the old one it did not appear dirty, but when I opened up the fins each one had 15-20 dead ladybugs in it. Should those little bastards be able to get in there? I did purchase some MAF sensor cleaner and just did that. Once it dries I will see if it made any difference.

 

[alpac]

I am thinking vacuum leak. I had a very similar issue with mine and it was a vacuum leak. The way I found the leak was by using carburetor cleaner spray and spray the hoses and vacuum connections. The engine reved up when I sprayed over the vacuum leak. It was one of these little plastic hose.

 

[parson2008]

im thinking idle control valve mine did the sME, I cleaned it and the m.a.f sensor and is fine now

 

[MikeWild]

I had a similar issue. Turns out the CPS was faulty. If all esle fails, might be something to look into. Good luck, I drove myself nuts until I figured it out.

 

[Otto]

Try replacing the EGR valve

If it's a vacuum leak, 80% chance the egr is clogged or stuck open