Rough Idle
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From: Casa Grande
Rough Idle
I have a 85 with the stock ignition and carb. In trying to get it to run like it should I have replaced plugs/wires/rotor/cap/ignition module/ coil/ O2 sensor/ intake gasket/ carb gasket. The carb is a about a year old and I "think" ok. It's running allot better but still not good. At idle up to about 1/4 throttle it is rough and almost sounds like I can hear a popping. 1/2 throttle on up it seems to run good. I've used up a couple cans of carb cleaner chasing vacuum leaks but, except for the intake, can't find anymore. Sense I replaced the TFI module it has no codes. I have ordered a vacuum gauge, no one had one in this little town, but don't have it yet. I've never used one so guess I'll learn. Any ideas what I could check next?
Also, could someone post a pic of what the timing mark looks like? I found the one on the right (passenger) side but have read in another thread it's the wrong one.
Also, could someone post a pic of what the timing mark looks like? I found the one on the right (passenger) side but have read in another thread it's the wrong one.
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Joined: Aug 2010
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From: Vancouver, WA
How many miles on the motor? You've done the most likely problem areas. I'm guessing that either the EGR is failing or you have a lifter or valve issue. Are you sure you routed the plug wires correctly, and not getting cross fire?
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From: Casa Grande
Thanks for the reply. I'm fairly sure the wires are right, but never hurts to recheck. Valve or lifter were kinda what I was thinking, but hoping not. No idea how many miles on it but from the condition of the interior I'm guessing allot. Hadn't even thought about the EGR valve but wouldn't that cause a code? Got to go pickup the vacuum gauge today maybe just get one of those to.
I know it got codes for the MAP, as well as the TFI, when I first started on it but they went away when the TFI was changed. It might still be bad but at almost $80 I don't want to change it just to find out.
I know it got codes for the MAP, as well as the TFI, when I first started on it but they went away when the TFI was changed. It might still be bad but at almost $80 I don't want to change it just to find out.
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From: Vancouver, WA
The vacuum gauge will tell you a lot about how your motor is working. There are post here somwhere about properly reading a vacuum gauge. Did you clear the old codes? I'm not sure you would get an EGR code on an 85.
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From: Florida
I see you asked about timing marks, and that is where I'd check. The timing tab will be mounted to the block on the 4.9 (It looks saw toothed) you will probably need to clean it to read it. But you should have a notch on the dampener pulley. As far as timing I'm not sure on an 85' but 87'-96' is 10 deg. BTDC check your emissions tag under the hood to be sure. Good luck and let us know how it goes. Also the MAP can cause this Issue BUT check timing first and vacuum lines.
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From: Casa Grande
Thanks for the replies. Yep cleared the codes after replacing the TFi and rechecked, no new codes. As far as the timing marks, I found the ones on the right side of the motor but another thread said those were the wrong ones and there were some on the left side of the motor. I don't know if that's all 300's or just newer EFI's. But doesn't appear that mine has that one so either it was removed or not needed. But will find out tomorrow for sure when I dig out the timing light. And maybe ought to recheck the codes and see if that MAP error came back to.
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From: Butler PA
i have a 1981 f150 with a 300 carbed engine with a simular problem. Off idle she runs smooth but at idle she stumbles a little. I replaced all vacum lines and it need a carb so I replace the carb. wires, plugs,cap, rotor, coil and module on the fender well are all new. She still studders on idle. I am out of Ideas what it could be and info?
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From: Casa Grande
Well got my vacuum gauge/ vacuum pump and did some checking. I used the meter to set the timing and that helped, no more popping sounds but still rough. The vacuum gauge shows 18 and steady. Ran it up to 20 then backed it off so timing should be good. Checked the vacuum port at the carb for the EGR, it showed 0 at idle and ran up to around 10 as I ran the RPMs up. But no vacuum at the EGR and can't build up any vacuumwith the pump connected to the EGR valve so think it's bad. But also think the relay on the valve cover is shot to. Man there's a lot of parts to this thing. Really hate to dump all the TFI stuff but getting tired of buying replacement parts for it to.
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Joined: Sep 2010
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From: California
Seems to me you may have answered your own question. Mines a 77 300 so I can't help with the TFI stuff but if you have a strong EGR signal at the carb but can't even open the valve with a vac pump....I'd check the valve first to see if it's just physically stuck. If it isn't, then that vacuum is going somewhere. That would also explain the RPM range your getting the rough stuff at. Just a thought. Oh, my timing marks are on the left side (passenger) of the dampener bolted on with 2 of the bolts that hold the timing cover on. If yours has one, it out to be pretty obvious. Maybe someone took it off or had the cover off and didn't put the indicator on when they reinstalled the cover. Either way, if you set your timing with a vacuum gauge then in my book, you did it the best way anyhow. good luck !
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From: Casa Grande
Welp, EGR is bad but so is the relay(?) on the side of the valve cover that controls it. EGR moves freely but not with vacuum so guess it has a hole in it. And the relay never switches vacuum to it. Pulled the carb and EGR spacer and replaced the gaskets but still leaking between the spacer and manifold. Think maybe the spacer is bad. I'll tell ya, going to a DSII and aftermarket intake is sounding better and better. It's amazing how much c**p there is in this system that can cause problems if it's not maintained. Got over $200 in replacement parts already and the EGR and MAP are going to be another $150-$200.
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