Simple question. Could a bad o2 cause high idle. Ran codes and have a very rich fuel blend. Said o2. When I did tune up oil change diffs changed trans flushed transfer case changed , the plugs were white. It idles high but when I apply breakes like as soon as truck like stops and leans back, the idle will drop to normal. Every stop is the same. I apply breaks, idleing like my foot is still on gas, then complete stop truck leans back, idle drops to normal. Soon as I get a chance I will replace rear gastank and I got a super 44 and gonna 45* it b4 rear tire. ( I kno I been saying I'm gonna real soon but I'm pressed for time last few weekends. I have parts jus no time) was also thiknking mabye its the brake booster. Idk codes showed very rich, and o2. 4git the codes I accidently tossed the paper out.

 

Replace your o2 sensor? my truck does the same thing since the exhaust rusted out before the sensor and then fell off.

 

No the O2 sensor won't cause a high idle and I'll bet the code you got didn't say "O2 sensor switching not detected" but instead siad something like "system at rich fuel adaptive limit", and if so that means you don't have a bad O2 you have a problem outside computer control that is making the motor run excessively lean.. which is verified by the white spark plugs. If the motor was actually running rich the plugs would be black.

So what is causing the motor to run lean? Could be an exhaust leak upstream of the O2 sensor caused by a cracked exhaust manifold or a rusted/broken smog tube, could also be a gasket leak on the intake or a vacuum leak, lots of possibilities.

 

Chases all vaccume lines n sprayed then no leaks. Exaust isn't leaking except the exaust was all holey after cat so I cut muffler n tail pipe off. Its straight out the cat. Only thing I see weird is the charcoal canister up front. Is there 2 tubes off it? On mine one is broke off but I can't find anything hanging to plug into it... also my dad thinkis the timing chain is loose. Says that's what's causing the high idle bc the timing is off. Bc the timing is off its throwing an o2 code. I don't kno. Truck is nickleing me...

 

There are a limited number of things that will cause a high idle.

TPS fault.. this should show up in the codes.
Sticking IAC valve.. some TB cleaner should fix that.
Vacuum leak.. could be hard to find, but one source for a large vacuum leak is the brake booster, and since your problem seems to change when the brakes are applied I'd investigate that.. maybe disconnect and plug the line going to the booster and see if the problem fixes itself.

 

Plug the line going to the booster? Won't that cause problems?

 

Plugging the line going to the booster will make the brakes hard and less effective, but it's only intended as a test not something you would leave that way. If your high idle problem goes away when you do this that confirms your booster is the source of the vacuum leak so replace it and put the vacuum line back on.

 

thanx i will try that out