Idle surging
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Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
Idle surging
I have a 92 F150 recently bought 302 manual 5sp 4X4 it has a cracked exhaust manifold on the pass. side actually in 2 places. Runs rough when cold but pretty smooth when warmed up. The cast iron exspands. Will replace the manifold when the weather warms up. Have a new one. Just recently the idle has been surging after it is warmed up and I get no codes with KOEO but code 42 for the O2 sensor with the key on engine running. I can smell the rich burning fuel. I know the manifold has some of the blame but looking for some othe Ideas to check when the weather will allow. BTW this is the greatest site.
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Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
I just replaced my alternater a couple days ago so I thought I knocked loose a vacuum line at first but they all looked good. I didn't check the vacuum canister to see if its holding vacuum. I will put a vacuum pump/gauge on it when I get a chance. It's -35 F wind chills outside right now. Maybe in a few days when it warms up. I did run some injector cleaner through it to see if that helps. Thanks for the info.
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Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
I checked my vacuum canister and it holds vacuum fine. I bought some trottle body cleaner and cleaned my throttle body. Now it doesn't surge anymore but my idle is really high. I think the next step is to replace the air/idle bypass valve. I have a new one off a 96 intake from my brothers crate motor. He ran a carb on it. It looks the same but Rockauto shows up to 93 are the same. I am going to try it and see what happens.
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Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
I replaced the air/idle bypass valve and no change. I have a whole new 96 5.8 throttle body with tps and everything else on it. I am thinking about switching it out for my 92 5.0 one. Does anyone know if its close enough to work ok. I will measure the holes and see if its the same. I have the intake and upper plenum also but I know they are different. I have the next 2 days off to play with it.
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Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
Well the 96 5.8 throttle body is the same except one coolant line is shorter and there are 2 more vacuum lines for the fuel carbon canister. I switched it out with the new carbon canister solenoid, tps and air/idle bypass valve. It fixed the fast idle and its a lot more responsive now. But the original problem of idle surging and running rich is back. I pulled the vacuum line off the fpr while running and no fuel. If I put my finger on the vacuum line it doesn't change how it runs at all either. I plan on pulling the codes again tomorrow and go from there. Any ideas? Leaking injector? The upper plenum has a lot of carbon build up in it. Might try the sea foam thing with putting it in the brake vacuum line. Never did that before. How do you guys do it?
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Thread Starter
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Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
Well I pulled the codes but had to clean up the connectors to the starter, since it didn't want to start when I tried it. I did get a different code on the scanner. I hadn't checked the slow codes only the fast ones. Well with the slow codes I got a 21 with KOEO and KOER so its a engine coolant temp out of range which makes sense with it running rich when warm. Haven't replaced it yet. I blew the brake line right by the gas tank last night so need to fix that first. Did put some sea foam in the vacuum system and ran it for a while. Will see if that helps or not.
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Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
I Replaced the bad brake line and bled the brakes today. So thats fixed. I replaced the ECT. Ran the code again. I get the pass code 11 for KOEO and just the 42 for O2 too rich on the KOER. I can smell its still too rich and its still surging. I really think the FPR is ok, no fuel, although haven't checked the fuel press. Need to buy one of those gauges. I am going to try the map sensor next. I have a spare off my old 84 tbird stuff and according to rockauto its the same part. Will keep you posted.
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Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
Well since then I have replaced my oil pan gasket that blew out and then the water pump started leaking. Pulled that off and broke 4 bolts. So took off the timing chain cover and got out the bolts. Also replaced the timing chain. Runs ok with no leaks now but still surges. I cleaned up the ground on the front radiator support by the window wash tank. But no change. I am going to pull the codes tomorrow again. I don't smell the rich smell anymore after I fixed the leaks so thinking the O2 sensor might be thinking its rich and leaning out the motor too much. If I get the same code, will change out the O2 sensor and see what happens. Will post it.
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Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
I replaced the O2 sensor, no change. Finally decided to replace the passenger side cracked exhaust manifold. Wasn't too bad. Didn't break any bolts to the head. And my 84 tbird 302 exhaust manifold was an exact fit. It even had the same casting #'s. Just had a O2 sensor on it. Just left that in to block the hole. So didn't have to buy one. Started it up, no leaks ran a lot better, but still surging. Sprayed some penatrant spray around the egr valve where the holes are and it smoothed out great. So I am pretty sure that is it. Was thinking about taking it off anyway. I am going to make a blocking plate and plug it off. Maybe buy that jumper for the position sensor. Next project.
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Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
Well today I bought a new fuel pressure regulator for my truck. Put it in and it runs and idles awesome. I had checked the vacuum line a bunch of times and no fuel before I changed it. Looked like the original ford one that was on it. Well just really happy its fixed along with my oil leaks, and water pump. The fpr was only $28 too. Just wanted to post this to help someone else out if they have the same problem.