Rough idle

[Epa4eye]

So, I’m pretty new to the foxbody game and I started having some trouble with my ‘85 carbed 302. It all started with a rough idle which would cause the motor to stall. I adjusted the idle mixture screws on the carb and I was able to correct the idle. I then noticed that the pcv valve was sucking in A LOT of air, whether it was idling or in gear driving down the street. While I was under the hood adjusting the idle screws, I decided to change the oil, install a new pcv valve (it was still sucking a lot of air), and new spark plugs (old spark plugs were semi fouled and had a little bit of oil on them). THEN, after driving the car a little down the block, I went to turn it on again after it was already warmed up, and it started making a loud cranking/grinding noise. Almost as if the transmission was grinding it’s gears at the same time it was cranking, and when I take the key out, it continues to crank and grind!! Please help lol

 

[broncojunkie]

The cranking/grinding thing is most likely the starter relay sticking OR the starter itself. It could audio be your ignition switch, but that doesn't normally cause this issue (still possible). To rule out the ignition switch, try this: Assuming you had to unhook the battery to get the cranking to stop, simply remove the small trigger wire from the stud on the starter relay (inner passenger fender). If you can hook the battery back up and it's not cranking, either the relay or starter freed up on its own or it was the ignition switch. If you hook the wire back up (key out of the ignition) and it starts cranking again, it's most likely the ignition switch.

You can test the relay with a meter. Looking at the two large cables hooked to the studs on the relay, unhook the one that goes down to the starter. Hook up the battery and see if there is power going to both studs (key off position). My guess is that you'll find power is crossing over. To help eliminate the key switch and connected wiring, remove the small trigger wire while doing this test. The relays are pretty cheap, so buy a good one and go ahead and replace it if you suspect it is bad.

Another point to make note of: The battery and starter cables and ground cables are old on these cars, unless they've been replaced. They may look good but usually have corrosion down inside the insulated area that you can't see. If the cables get bad enough, they can cause damage to other parts....typically starting systems and ignition parts (starters,relays, ignition coils, distributors, etc). Plan on replacing them if they're old.

 

[Epa4eye]

Thank you! I will definitely be trying everything you mentioned.

Any idea as to why the pcv valve was sucking in so much air? It doesn’t seem like the pcv valve and the cranking of the engine would be related, but I did notice that happening first. As well as the somewhat fouled spark plugs.

 

[broncojunkie]

I don't recall how the 85's pcv system was set up, but I'm presuming your pcv is on one valve cover and there is a breather cap of some sort on the opposite valve cover? If so, make sure there isn't something wrong with the opposite side. I think the older cars had a breather cap with a hose fitting.... and that hose was routed to the back of the air cleaner housing. If that's how yours is set up, make sure the hose isn't clogged or pinched. You can probably remove the breather cap altogether for testing and see if that fixes your problem.

There should be some vacuum diagrams available online that may help

 

[Epa4eye]

That’s correct. I swapped out the pcv valve for an actual breather cap and capped the pcv port on the carburetor, so I’m hoping that solves that issue.