Hello Everyone, I'll be quick to not waste too much time:

I just came back from the shop after having a new rebuilt transmission installed. I also had my heater hose replaced because it was bad. After getting all the things I needed done I was told by the shop that I had bad sparks and that my engine was misfiring. I knew that to be the case, but it wasn't ever too bad. I told them not to do the replacement because it was very expensive and sparks are relatively easy to fix.

I just got my car back an hour ago and it is vibrating very rough at idle-to-low rpms. It always had that problem, but never to the extent is has now. Given the things they might have inspected, could it be that they put the sparks back in incorrectly or that there may be a problem with the heater hose or perhaps something else?

Thanks for y'all's responses!

 

The shop would have disconnected the battery during the procedure. That erased the truck's stored fuel and ignition tables. The manual calls for the engine to idle for 20 minutes anytime the battery is disconnected to reestablish the base line for the individual vehicle. If your plugs were bad to start with the ECM is having problems adjusting the base parameters to match expectations. Unfortunately, you will need to address the known issues before you can determine if the shop revealed/caused anything else.

 

Welcome to the forum

We assume a Ford Ranger
What year?
What engine?

rcr4v3n has a good point about computer being reset and having to relearn some engine parameters.

Depending on what engine you have I would also check spark plug firing order, very very easy to miswire that.
Does the engine run OK, no missing, at higher RPMs?

No, on the heater hose, outside of overheating it can't cause engine problems

 

I drive a Ford Ranger XLT 3.0L 2002. Sorry, I thought that information came up on my profile, just made the profile so not sure how that works here :/.

I see, that could make sense. I'll turn it on and let it run for a bit tomorrow. Regardless, I'll probably do the spark plugs with the wires myself tomorrow as well. I knew it's about time these get looked into anyway.

 

Thanks, I tried that today and nothing came of it, but I had no idea that it might be a problem.

Ranger XLT 3.0 2002. It seems to run fine at higher RPMs. I haven't really been able to tell if there is misfiring. I'd have to drive it a bit more to find out. I don't know how to check the spark plug firing order... can I find that information on this website or in my manual?

 

If it runs fine at higher RPMs then firing order is OK

If engine vibrates at idle then it is misfiring

I would change the spark plugs, regular copper or Double platinum, never single platinum in a Ford

But you can check for a vacuum leak for now.

On the upper intake you will need to locate your IAC(idle air control) Valve
Picture of one here: http://i665.photobucket.com/albums/v...acvalve005.jpg

Will look similar on a 3.0l, can be on drivers side or passenger side of upper intake
It has a 2 wire connector that you will need to unplug while engine is idling, so unplug it now while engine is off so you know how to do it, then plug it back in.

The IAC Valve is what the computer uses to set a stable idle for a fuel injected engine, idle screws won't work, computer needs active control of air flow to set idle.

You need to do this vacuum leak test after engine is fully warmed up, so after you come home from work or after running an errand.
leave engine idling and open the hood
Unplug IAC Valves wires

IAC Valve will close and engine RPMs will drop to 500 or so, engine may even stall, either is GOOD, it means no vacuum leaks.
If idle stays high, no drop, then you have a vacuum leak for sure

 

​​​​​​So i did what you recommended; there was a drop in RPM when i disconnected. When i reconnected it would rise up really fast. I now have a check engine light on, but I'm pretty sure its from the IAC

 

Thats good, so you know there is no vacuum leak causing the misfire

Yes, IAC valve caused CEL(check engine light) it should go off on its own after a few drive cycles, if not then disconnected battery for 5 minutes or so.

Plan on changing the spark plugs
Regular copper or Double Platinum, never single platinum in a Ford
And keep track of which cylinder the old sparks plug come from
You will want to inspect the tips to see if you can see an issue for the misfires
Google: Spark plugs tips

Lots of pictures of what the tip colors mean, and you will usually see one or two of your plugs "do not look like the others", write down which cylinders those plugs are from and save it, may be helpful if misfires come back

Also I put a can of Seafoam or similar, fuel system cleaner, in the gas tank once a year.
Fuel injector tips spray fuel out to get best mix with the air, but the tips can get dirty over the years.
At idle or lower RPMs the fuel injectors are not open very long, so if tip is dirty the fuel can Drip out, instead of spray out, this causes poor mix with the air, so can cause a misfire.
For the $6 I think it is worth it, my engine seems to idle smoother about 1/2 way through that tank, but could just be my imagination.