Well I'm finally back to messing around with my 7 after being out of the country for many years.

Before leaving, I had the engine ported with new housings and rotors. I put about 20,000 miles on it and it ran flawlessly. After driving it to my parents it was placed in hibernation.

When I got back, fluid change all the way around from coolant to diff. New plugs, wires, and filters all around. Replaced a few bad sensors, water thermo switch and water temp sensor. Inspected everything I could, in section 4 of the FSM. Checked the compression, still in the low 90's and even. Really took my time and relished the activity.

Went out for a test run and it was running okay, but it was just not pulling like I remembered. Checked the injectors, because it was the only thing I hadn't checked, and sure enough the primaries were clogged, replaced them.

Now it pulls like a beast, but just won't idle right. I have checked everything I can think of. I'm probably forgetting something simple so I thought I would get a second opinion from here.

On some days, when the weather is right, it idles great, nice even exhaust tone, no misses or pulses.

Other days it waves from 600 to 750rpm. The break switch seems to effect it, if I let up the break pedal at a light it will sometimes stop waving, pressing on the break again changes the idle, but the break effect is intermittent.

It will also idle choppy at times. Stumbling or missing, the exhaust tone stumbles.

Adjusting the variable resistor from lean to rich it gets worse, the only place it will idle at any setting is full lean. I checked for vacuum leaks and even replaced a few hoses just to be sure. Removing the BAC connector makes the idle worse. I haven't put any extra grounding in but I checked all the existing grounds and they seem to be okay.

I think I remember back when I had the motor built, Scott asked if I wanted a smooth idle port or a rough idle port. I'm not sure if this is my mind playing tricks with me or an actual memory, it was a long time ago. Now I'm wondering what part this would play.

I'm thinking it is most likely a fuel management problem, due to the full lean setting on the variable resistor, but could be wrong. Or could the 5th gear switch be causing my problems? I can't get under there to check.

Sorry for the long post, but i wanted to be thorough. I'm racking my brain on this. Any ideas would be helpful.

Thanks

 

TPS sensor maybe? that would be a minor surge issue. mine would do it. I didnt care much at all and left it like that for awhile

 

have you removed any idle or emissions control systems from the vehicle?

 

The TPS is adjusted, although it took some time for it to find it's home. But now its fine.

All the emissions stuff is still there, nothing from that system has been removed. Air pump and ACV still function correctly, even the Aux port actuators work between 8 and 14 psi fully open.

There is no 3800rpm hesitation at all.

Thanks for the replies.

Anyone else care to take a stab?

 

Try bleeding the air valve from the throttle body

 

Bleeding the air valve from the throttle body produces a higher idle, around 900rpms and it's smooth. Could that mean something is clogged?

Update on the drive this morning, the wave in the idle is 750 to 850rpms.

 

I'll venture a guess. The brake pedal sounds like it may be an air leak in the line from the booster to the block maybe? But then again it could just be the voltage difference when the brake light is on/off/on, and since this happens intermittently that could be a little electrical gremlin. My next thought is neutral switch, jack her up and see.

 

Could very well be an electrical problem, the voltage at idle from the alt is not steady, when it is acting up.

ATM I have the main e-fan off and the small aux fan on at 190. Its cool enough outside that I don't need the big fan yet.

I'm thinking about doing the taurus alt upgrade that everyone is talking about these days, and adding extra grounding, just to see if it is a lack of voltage causing the problem.

I keep searching the site for issues like this and noting comes at me, but there are a lot of posts to look through. If someone knows of a similar issue that was resolved, please post a link, that would be helpful in my searching this out.

the only real mods I've done to this thing other than the engine has been the koyo radiator, the e-fan from a fiero, RB exhaust mid-pipe to mufflers, and auto to manual transmission swap. But all of that was done many years ago.

Thanks for the ideas everyone.

 

On the way home this afternoon, it started smoking at a stop light, not a lot but enough to notice in the rear view. After taking off, it cleared out, then the idle was great. It was oil smoke for sure, the smell and the look of it was unmistakable.

It seems that something might be sticking up. I'm not sure what though.

Looks like I'll be pulling the Intake off again. I'll replace the rest of the hoses, add an engine ground and tie it to the chassis, retest every emissions part, and swap the injectors around, just for kicks. We will see if that does anything. If not back to 0.

As for getting the car in the air, I'm back at school now and I don't have access to the same stuff I would have at home.

 

The first thing I check on cars with that sort of idle issue is the BAC, if that looks OK then most of the time it's a vac leak.

 

Thanks SonicRat, I'll be checking that out again.

When I pull the plug on the BAC it changes the idle, not in a good way. When I set the initial coupler it idles higher, but not good either. So I assumed it was okay. I'll test it per the FSM on Saturday.

I've triple checked every vacuum line on the system. However I'm going to replace a few of them as they are a little old and should be changed anyway.