I recently put dual exhaust on my bronco and now my engine idles up to 1500-2000 rpm by itself. I have put a new oxygen sensor in and other sensors that deal with the exhaust and throttle body but I still have the problem. do you have any ideas?
Q&AAsk Your Question
1990 Ford Bronco
Question: engine idles up on its own
Answer #1irvtech March 18, 2010, 20:36Journeyman
I have to assume that this was not happening prior to the exhaust work.The two most likely problems are an unmetered air leak, like intake manifold plenum gasket, cracked vacuum hoses or the wrong PCV valve. If you hear a lot of hissing in the area of the PCV valve you may have the wrong one, get a Motorcraft one and try it, that is the cheapest and easiest thing to try. The other thing could be the the throttle body, since you replaced that. Was this a new or used part?On the throttle body is a valve with a two wire connector, the valve is cylindrical with a flat base and two bolts holding it in place. If you unplug this valve with the motor running and the valve is functioning properly, the engine should slow down. These valves can get stuck and make the idle stay high. These are your first things to check, let me know the results and I can try to help you further. Good luck.
Answer #2Visitor, March 25, 2010, 17:22
i checked the idle air position sensor(purchased new) by removing the wire connector while the engine was running and it idled down to 700-800 rpms and then i reconnected it and it idled back up to around 1300 rpms then dropped back down to 1000 rpms.
the problem all started when i converted my exhaust from a single to dual exhaust and NO catylatic converters. i have a new oxygen sensor in passenger side
next, i replcaed was the coolant temperature sensor which is mounted in the lower intake manifold (which was leaking slightly) close to the distributor.
I did not replace the throttle body, it is original.
I did these repairs after I had a friend of mine who is an ASE certified mechanic put a diagonstic computer on my bronco and it gave me several codes.
I just replaced the EGR tube which was broken and am still having the engine idle up around 1000 rpms.