RENIX 4.0 idling low when warm, also having hard starts at all temps

Ok, so, I've spent the last several days trying to troubleshoot my misbehaving engine.

Long story short, it's idling at the happy 750-800ish range until the engine warms up, at which point it idles at more like 400-600.

As well, regardless of temperature, it seems to have trouble starting. The starter chugs away just fine, but it take the engine a good 2-3 seconds of cranking before it fires. Then, once it's going, the idle sinks down to around 200 in the next couple of seconds, and either dies, or works its way back up to 750 after a few seconds. If it dies, and I try starting it again, it fires almost immediately, and revs itself up to 1500 for a few seconds, and then eases down to 750 (until it gets warm, and starts to fall).

I've done a lot of reading, and tried several things to diagnose/fix this, so here's the list of things I've actually done. None of these made a noticeable difference of any kind.

- Replaced the plugs/wires/cap/rotor/air filter about 500 miles ago (it actually runs noticeably better since doing this, but it still idles funny).
- Cleaned the throttle body out with carb cleaner (which I now know is Very Bad, and might think was the source of my problems, if it hadn't been doing this since before cleaning the TB out)
- Tried running it with the latch relay removed.
- Tightened some loose bolts along the top of the intake manifold (it was actually idling high when warm, before I did this)
- Put a few loose vacuum hoses and electrical plugs back in place, which I found while monkeying around under the hood.
- Disconnected the IAC once it was idling at 750 (it fell down to 500 anyway, once it warmed up).
- Each time I screwed with one of these things, I reset the ECU by disconnecting the battery, then driving around like a madman to go through the whole range of throttle settings, followed by killing the engine and restarting.

So, because it seems related to the temperature, I'm hesitant to just replace the TPS or CPS, and since it's not giving me any CELs through any of this, it doesn't seem like my sensors are to blame.

One thing I did think of, though, is my nasty old battery cables. Often, while running, my dash volt meter only shows around 12.5 volts (but goes up to 13.5 sometimes, without any clear connection to weather or anything). I cleaned the hell out of my battery contacts, and it didn't change.

Any ideas?

Sounds like your IAC needs a thorough cleaning and then tested.

Renix engine has to crank up to approx 300 RPM before it will fire off. If your battery is weak or the starter it will increase the cranking time.

Sometimes adding a fuel line check valve back by the filter will help some.

Hey man, I had some similar issues with erratic idle recently. I pulled the IAC valve off the throttle body and it was pretty caked with carbon. Try taking some brake parts cleaner or mineral spirits on a cloth and clean the carbon off. This totally fixed the erratic idle issue. I have yet to totally fix my starting problem, but mine only has trouble starting when its cold. But it always fires up and runs good. Let me know if you fix your hard starting issue.

Ray

I just thought of one more thing. I went ahead and pulled the whole throttle body off and cleaned it as well. Make sure you clean the cavity where the IAC valve seats inside the throttle body for it as well may have a bunch of carbon buildup.

Thanks for the replies. I'll try cleaning everything in the throttle body.

Hey man, I read a thread on another site, sorry no link, that pretty much said for the hard starting we are going to have either leaking injectors or a bad check valve in the fuel pump, or both. Either way, the car sits and the fuel pressure bleeds back off into the tank which causes a lack of fuel to the engine for a couple seconds until the fuel is pumped back up to the injectors. Replace fuel pump and see if that helps.

Rayford said:

Hey man, I read a thread on another site, sorry no link, that pretty much said for the hard starting we are going to have either leaking injectors or a bad check valve in the fuel pump, or both. Either way, the car sits and the fuel pressure bleeds back off into the tank which causes a lack of fuel to the engine for a couple seconds until the fuel is pumped back up to the injectors. Replace fuel pump and see if that helps.

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I would put a check valve in the fuel line, $14 + cost of two clamps, before I would pop $70+ dollars for a new fuel pump.

As for the injectors, if you haven't already done the Ford injector upgrade it might be a good time to consider it. You could drive it, park it, wait a few hours and then pull the spark plugs to see if any are wet with fuel--not a for sure test for leaking injectors.

I'm doubtful of my injectors being a problem; it did the hard starting when I bought the jeep last fall, and it did it just the same after I had to replace all the injectors in February this year (I had the infamous 1990 injectors that will suddenly start belching fuel directly onto to intake manifold).