What would cause my car to skip at low RPM's

[davmacdon]

I started testing conectors from the ICM to the computer and the spout to the computer and all is well. I took the car out to try the old "run it hard and it will fix itself" concept. That did not work either. While I was out I thought I would look for any arcing of wires and plugs, so I go to a dark cul-de-sac, open the hood and WOW, it looks like christmas lights under the hood. Everything is arcing plug boots to headers, plugboots across plugs to block, wires to block.

I put some cheap wires on to see if wires were the problem and might have created more of a problem. Since I disconnected and tested all of the connectors(PCM,ICM,SPOUT) I have not got the 212 error code again. HMMMMM...

What would cause such severe arcing?

 

[Venom4.6]

Check all the ground wires. Use a wire brush and clean them all up including the surface and bolts/nuts.

 

[romgolferman]

i have just about the same problem in an 86 bronco with a 5.0. goes to 1500 rpms and then cuts out till it gets to 1000 rpms and then kicks in again. im going crazy. ive done the same as everyone else. ya know plugs, wires and even a timing chain. someone please help. it is driving me nuts

 

[romgolferman]

bump

bump

 

[89ripper]

ok my car used to buck extremely bad when i tried to maintain speed or hold the throttle in one spot, usually around 2500rpms or so, i though it was throttle postition sensor, egr valve, distributor, so i just started to throw money at it, nothing fixed it, i just happened to check my air filter ( i have a cold air intake) and it was gone. i replaced the filter, and the problem went away, dont know how or why this would be related to that but it fixed it, so it would be worth a look

 

[davmacdon]

I work at our familys GM dealership and will be bringing my 5.0 in and put it on the scope to try to pinpoint the problem. I am the blacksheep of the family, I have 3 Fords and no GM vehicles. I will post the results of the scoping.

 

[davmacdon]

OK, I put the car on the scope at work and it showed that the problem is with the primary side. All of the cyls drop out at once. I put a new coil on it and still had the same problem. I checked all the grounds again and no problems there. I guess the only thing left now is the pickup on the dist or a whole new dist.

Any suggestions?

 

[davmacdon]

Finally found the problem. It was a loose pickup in the distributor. It was bolted down but still had play and was hitting the inside of the vane/shutter thingy as it spun. It was hard to see unless you took it out. It might be worth it to check the pickup for play on some of these mystery misfires.

 

[Supaman]

Does everything run perfect now?

 

[davmacdon]

Yeah it runs like a champ. Even starts better. I took it our and had a little RAG-A-RAMA session and no misfires at all.

 

[shttygtstang]

ttt

 

[Supaman]

Could you give me a step by step diagram on how you did this. I am having the same problem that you had and I'm not really mechanically inclined. Any help will be greatly appreciated. Thanks.

 

[IndyBlk5.0]

Anyone know what an idle air control does???? think about it..
very low rpms........ hummmmm.

 

[davmacdon]

I would first remove cap and rotor and then remove the vane/shutter (the thing that the rotor goes on) it is held in place by two 1/4" nuts. Once you have it off look at the inside edge to see if it has been contacting the pickup(mine looked good on the outside but when I removed it I could see the damage). The pickup is the black plastic thing that the vane/shutter goes through as it spins. My problem was the pickup was loose and was rubbing against the inside of the vane/shutter. A lot of play in the distributor shaft or if one of the vanes were bent could cause the same thing.

I looked about everywhere else for the misfire including checking all the grounds to the engine and the computer. New wires, cap, rotor and coil. I had looked at the distributor but it had no play and look good from the outside.

Hope this helps...

 

[Supaman]

So the vane/shutter is not supposed to be touching anything, is this right? When I removed mine all the shutter thingy was all gouged up except for one. Did you just replace it or get a whole new distributor? Thanks again.

 

[blk92stangg]

Not sure how relevant this will be for you guys, but I used to have a stumble right off of idle. Reading a book pertaining to tuning EFI ford's, it recommended adjusting the minimum idle air bypass...Meaning that while the computer is the one that ultimately decides on the idle rpm, you are able to control how much air is allowed to flow past the throttle when it is closed. If there is not enough air passing at idle, the IAC valve is forced to cycle at a higher frequency to allow enough air to let the car idle, which somehow causes hesistation, bucking, and supposedly stalling upon decleration. You basically need to reset the idle by unplugging the iac, setting the idle rpm to around 7-800 or so, and reconnecting the iac(make sure you reset the ECU too). If the car revs too high when you reconnect the IAC, it may be bad. The idle should not change when the IAC is reconnected, since the IAC only should increase air flow when a load is placed on the enging by accessories to keep the car from stalling. We have so far tried this on 2 cars, encountered 1 bad IAC, and so far the results are promising. If you have crazy vacuum leaks, funky fuel pressure or other problems that circumvent the throttle, the above will probably do nothing for you. As always, YMWV.

Idle adjustment

 

[davmacdon]

Supaman, I don't think the vane/shutter is suposed to contact anything. The vane/shutter is just supposed to disrupt the magnatic field as it passes through the pickup(Hall effect). I took my distributor apart and was going to rebuild it but no one sold the the vane/shutter by itself(I guess its part of the dist.). I bought a new distributor it was about $100 and included the vane/shutter as well at the pickup. It took about 20 minutes to install and the problem was gone. In my case the missfires would happen at really weird times. Sometimes I could drive it for a day and it ran perfect. Sometimes it would misfire every other startup in the same day.

Do you notice any fine black dust or metal shavings in the dist or attached to the pickup like a fuzz? Can you move yoor pickup around at all?

 

[95 5.0 'Stang]

I know this is an old thread but I just started having close to the same problems. When the car is cold, it skips and bucks like crazy until I get to normal operating temperature. The whole ignition system on the car is brand new MSD everything except Motorcraft plugs. It just started doing this. Anyone with any ideas as to why?