New Engine Idles Rough

[LSUMurse]

I took out my 307 and put a new GM 350 crate engine in. It has the Holley aftermarket throttle body. I did the initial break in and have had it out on the freeway a few times. It initially had some issues with rough running to the point that it would not stay running unless it was revved up. That was cured with finding a vacuum leak. It was miss firing in high RPM's. That was cured with a timing adjustment (it was at 16* BTDC, now it's at 9*. I guess I didn't tighten the bolt enough and it walked).

The thing I can't seem to figure out is the rough running in idle. I've cranked up the idle speed to 1100 when in nuetral to try to compensate. The idle speed when I shift into gear will drop down to about 600. This seems too low to me, but 1100 in neutral seems high.

It smells like it's running rich, but when I try to lean it out it runs rougher. I do have exhaust leaks on both sides between the exhaust manifold and pipes. I assumed this was due to me not disconnecting the manifolds from the pipes during the swap, however it does spit out some black sooty stuff from the exhaust now, something it never has done before.

Link to the system I bought:
http://www.jegs.com/i/Chevrolet-Perf...353K3/10002/-1

I also replaced the starter, water pump, and alternator.

I have exhausted my knowledge base on what to try next. Any suggestions would be appreciated.

[oklalawnboy]

I would call Jegs tech support.

[Unionwelder]

I'm not sure about the new motors but I had a 350 in my truck that the distributor hold down would not stay tight. I would adjust it ad it would rattle right back around after a few min. Not saying that's what your issues are but the symptoms are very similar.

[hugger6933]

If you got a chrome dist hold down I would recheck the timing again and check again for vac leaks. It still sounds like you may have a vac leak. You may want to spray some carb cleaner along the manifold rails and around the base of the EFI unit to make sure it is sealed. Jim

[mmiddle]

OH, I see what you did there! The Holley EFI system. OK, I do not have direct knowledge of this system, but Something is not "LEARNED" correctly. The system is dumping fuel at idle.
You might have already done this, but 20 years of troubleshooting robotics and industrial electronics tells me to start at square ONE and check all the dummy stuff first. Jegs tech support is going to have you do this anyway.
Pull out the install manual and start over re-tracing every step to make double sure you did not screw up.
I do technical support now and trust me.... it is always something simple that got over looked.

[LSUMurse]

I haven't had time to fool with her, yet. But, there was a new development. The other day when I went to shift, the tranny made a noise similar to the noise you get if you forget the engine is running and engauge the starter, while it was shifting. Could this be indicative of a vacuum leak? Maybe that is what the idle problem is related to (like someone suggested). It only did it on the first shift into reverse and then into drive.

[68gmsee]

Not sure about the noise when shifting, but as mmiddle mentioned the running rough, black sooty stuff out the exhaust sounds like running rich. I'd concentrate on that first. You should see the dark gray smoke coming out the exhaust.

The vacuum leak possibility can be checked fairly easy with a short piece of garden hose (my favorite stethoscope) or by plugging all the intake and carb vacuum lines and checking the idle again.

[homemade87]

Originally Posted by LSUMurse

I haven't had time to fool with her, yet. But, there was a new development. The other day when I went to shift, the tranny made a noise similar to the noise you get if you forget the engine is running and engauge the starter, while it was shifting. Could this be indicative of a vacuum leak? Maybe that is what the idle problem is related to (like someone suggested). It only did it on the first shift into reverse and then into drive.

That sounds strange. I dont know how it could happen because they are on the oppisosit side if the engine , I would clime under and check wires to linkage to see if you have a starter wire in contact with your linkage. Maybe something over the steering column.

[storm9c1]

The other day when I went to shift, the tranny made a noise similar to the noise you get if you forget the engine is running and engauge the starter, while it was shifting. Could this be indicative of a vacuum leak? Maybe that is what the idle problem is related to (like someone suggested). It only did it on the first shift into reverse and then into drive.

If you have a neutral safety switch at the base of the column where it meets the firewall (stock on a 67-72), I've had one fail oddly. The plastic (or bake-a-lite?) cracked into pieces internally and the metal "contacts" were shorting between the powered reverse light circuit and the neutral safety circuit (thus engaging the starter solenoid). That made the starter grind for a moment when shifting from reverse to drive or vice versa. It only happened sometimes, but it was a WEIRD failure mode. I replaced the switch and the problem was solved. Scared the crap out of me each time it happened too. And was certainly a safety issue.

Another possibility is that you may have heard pump whine for a moment internally in the transmission. I've had various transmissions do this after a cold start over the years, usually only happens for a moment (approx 1 second), and usually only happens once per drive, but is not consistently reproduced unless the pump is going bad or some other problem. This won't sound like a starter grind, it will sound more like a power steering pump groan.