I have a 94 Runner, manual, 3VZE motor that idles rough, gets approx 14 MPG max, and accelerates very poorly. It failed the smog check for a grossly high hydrocarbon count and the test actually couldn't complete because it was idling so rough.

I suspect there are a few issues at hand, but wanted to query the body of experience before removing/replacing parts. I imagine the TPS may be at fault to some degree, in conjunction with the O2 sensor right before the Cat. The truck seems to be running rich, which would lead me to believe that perhaps the excess fuel may have fouled the cat so much it needs to be replaced. I've read many similar posts on this forum, but can't come to a solid conclusion as to whether I should look into the air flow meter as well. I've heard some contributions laying fault on bad ignition coils and reed/EGR valves.

So to list the possible causes I came up with,

- TPS
- O2 sensor
- Cat
- Air flow meter
- EGR valve leaking
- Ignition coil bad

Do these sound like valid causes? If so, is there an order I should attempt to fix them in, or a recommended diagnostic checklist I could run through? Thanks.

 

check the ignition system too. spark plugs gaped properly and in good shape. check plug wires, coil, cap and rotor too. if in doubt with any of that get new OEM. lots of aftermarket stuff is junk. pulling out and inspecting a spark plug can tell you alot about whats going on in your engine. a plugged cat can also cause it to run like crap too.

 

A good proper tune up is always a good place to start. While you have the plugs out for changing go ahead and run a compression test. A rough idle could be as easy a vacuum leak or as difficult as a head gasket.

 

I've dealt with this issue for a long time.I pulled the temp sensor,AFM,anfd TPS connections and cleaned all of the cennetions. I mounted a NEW Knock sensor in the engine lift hook,and added a new pigtail.Added a new ground from the battery to the engine,and to the frame and chassis.Of course did a major tune up.
I clean the Throttle body with the sea foam Throttle body cleaner, not the pour bottle but a areasol cleaner they sell.I hads to special order it.The bigget problem I found was in bad connections,mainly at the AFM.I claeaned them and then bent tem to make sure I had good contact.

 

Thanks for the inputs. My deployment is almost over and when I get home, I'll post what I find.