Hey all, I had a question about one of my injectors in my TB. I'm trying to figure out my rough surging idle still. I already replaced and adjusted the IAC, also tested my TPS, which is perfect. On the IAC, when I unplug it and the engine is running, there is no change at all.. But I did a search on here and someone had said that's normal, that the pintle won't move when it's unplugged which would make the idle not change. Anyways, back to my question on the injector. If I unplug the injector on the passenger side of the TB, the engine gets real rough, but continues to run. If I unplug the injector on the drivers side, the engine stalls. Does anyone know if this is normal? I would think the engine should stay running if I unplug the one on the drivers side just like it does with the passenger side injector.

Also, the car has plenty of power. I've done a full tune-up. Plugs, wires, cap, rotor, fuel filter and PCV valve. I'm just trying to track down this stupid rough surging idle. If you guys could give me any advice, I would really appreciate it. Oh, I also forgot to mention, it's a 91 firebird 5.0L TBI. Just purchased it and it's my first one. Fell in love with the car right away, just trying to get the kinks worked out of it.

 

Surging is usually due to the engine being too lean. This could be caused by a weak fuel pump, plugged filter, plugged injector, bad O2 sensor, vacuum leak, IAC valve, etc..

Get a gauge and check the pressure would be a place to start. If you don't want to do that, take a timing light and flash it at each injector. This makes the spray more visible and you'll want to look for differences between the two. You can also take a bottle of propane (the small bottles usually used for plumbing) and go around places that could leak vacuum. If you have a vacuum leak, the idle will change a little.

I'm not a mechanic, but this is what I know how to do. I'm sure someone else will chime in soon with other ideas.

 

Your EGR valve could be leaking, which can give you a funky idle. Search the many posts here on checking your EGR valve.

Also take a look at your injectors during idle, you should see a nice conical spray of fuel. If you see any dribbling you have a bad injector or leaky o-ring. You can also look for the dribbling right before you fire the engine up (right after the ignition is turned on) and right after you shut it down.

Paul T.

 

Thanks for the reply guys. I forgot to mention, I already changed the oxygen sensor. I'm thinking the fuel pump is probably fine, because I have plenty of power, and I have no issues in the upper RPM range. No stumbling or anything. I don't know though, can a fuel pump only cause problems when idling but supply enough fuel for higher rpm's? I've looked over all the vacuum lines, they all seem to be in good shape and not leaking. I'm not too sure about the EGR valve though, I guess I should check that and my injectors next.

 

Ok, I just rebuilt the throttle body. I really gave it a good cleaning and inspected everything. It all looks to be in pretty good shape. I put it all back together, and put it on the car. It started idling even worse, so I readjusted the IAC valve and it's running much better now. Still a little rough, but I think I need to get my injectors cleaned.

Is WitchHunter pretty much the best place around to do this kind of service? I was looking on their website, and the prices seem pretty reasonable.