LT-1 hard starting problem

[walterlaughlin]

Originally Posted by Table Rocker

The IAC is located on the bottom of the throttle body. Here is a pic of one from a Z28:
http://www.shbox.com/1/iac3.jpg

Also, I believe you have to adjust the IAC position after you change it out so it knows where it is. I found this, but I have no idea if this is how it is done on our boats:
Depress accelerator slightly
Start engine, then release accelerator pedal, run engine for 5 seconds
Turn ignition "OFF" for ten seconds
Restart engine and check for proper idle operation
It is NOT recommended to to push or pull on the pintle of an IAC that has been in service. The force required can damage the threads on the worm drive. Also, do not soak the IAC in any liquid cleaner or solvent, as damage may result. When installing a new IAC, you may move the pintle to match the measurement of the old one. The force required to move a NEW valve will not cause damage to it. Use engine oil to lubricate the o-ring. Tighten attaching screws to 27 lb. in.

http://shbox.com/1/4th_gen_tech2.html
__________________

Hello sir, I just picked up a new IAC for my 95 LT-1 and it did not come with a flat paper gasket as I assumed it would, it only came with a round ring gasket that goes around the base of the pintle. Do I need a flat gasket or am I good to go with the ring gasket? Thanks!

[Table Rocker]

Originally Posted by walterlaughlin

Hello sir, I just picked up a new IAC for my 95 LT-1 and it did not come with a flat paper gasket as I assumed it would, it only came with a round ring gasket that goes around the base of the pintle. Do I need a flat gasket or am I good to go with the ring gasket? Thanks!

I have never changed mine, so I have no idea. I would guess that the o-ring would do the job and if you needed the paper gasket it would be included, but who knows?

As long as the o-ring seats and seals well, I would probably give it a go. I don't see a source for the paper gasket anyway.

[towelshoot]

No other gasket needed other than the o-ring seal it comes with. Easy Peasy as long as you don't drop the screw

[Jerseydave]

I read somewhere that you should wipe some motor oil on the o-ring before install. It didn't mention anything about a gasket so I assume there isn't one.

Going to have to try a new IAC on mine next week and see if that cures my hard starting.
For the little cost it's worth it just to have another new part on the 20 year old engine!

[gotta_ski]

The procedure above from Table Rocker is correct. I pulled mine out to clean it last summer and must have moved it a bit in the process. Boat would only start if I pushed the throttle forward in neutral after I put the IAC back in. A day of internet searching to find the above procedure and everything is now back to normal and the boat starts perfect.

[JimN]

Originally Posted by jakethebt

I have an LT-1 and had no idea it had an IACV. I will look tonight. If the LT-1 does, then it could be causing issues. It chokes the air down just like a manual choke. So when it is cold outside, it will restrict a lot of air. When it is hot out side, it will let a lot of air in.

As for location, it will have to be between the air filter and the cold air intake on the engine. They usually have some type of air restriction, either butterfly valve or needle and seat type. They usually have some type of vac or electric control on them. Since this is controlled by a computer, I would look for it to be electric and have a wiring harness.

Just saying... I can not confirm this is your issue, at this time I can only help you with the IACV, if there is one. My LT-1 started a bit hard this past weekend, but I am still on old gas. If it gets worse, I will be watching what you guys are doing.

Most injected engines have a way to maintain idle that's not the throttle plate. They don't have a choke, so the IAC and home setting for the throttle plate act as the choke by closing more when the temperature is low and opening when the temperature is high, as you posted.

The easiest way to find a lot of this stuff is by using Google. In many cases, it will direct you here (assuming you mention marine or Mastercraft).

[Jerseydave]

kpickett, any updates? Did you fix your hard start problem?

[kpickett]

Well, it's better, but not quite solved. I tested the fuel pressure at prime, idle, WOT, and for a leak down. It's all perfect. I checked my temp sending unit, and it's fine. I realized there was some corrosion in the plug wires, and I just replaced them yesterday. I replaced the IAC valve, and it's definitely smoother out of idle.

My friend who helped me with the fuel pressure tests thought it sounded like the starter wasn't turning fast enough. You could hear the starter bog down, then spin up to speed, so I took the starter to an electrical shop. They bench tested it and pulled it apart, and it's perfect. BUT, we realized that the brand new battery seemed to be only around 10.5 or 11 volts when it was hot. I'm exchanging it today. I'll let you know what happens. It needed the plug wires and the IAC anyway, and it's running really smoothly now.

[JimN]

Originally Posted by kpickett

Well, it's better, but not quite solved. I tested the fuel pressure at prime, idle, WOT, and for a leak down. It's all perfect. I checked my temp sending unit, and it's fine. I realized there was some corrosion in the plug wires, and I just replaced them yesterday. I replaced the IAC valve, and it's definitely smoother out of idle.

My friend who helped me with the fuel pressure tests thought it sounded like the starter wasn't turning fast enough. You could hear the starter bog down, then spin up to speed, so I took the starter to an electrical shop. They bench tested it and pulled it apart, and it's perfect. BUT, we realized that the brand new battery seemed to be only around 10.5 or 11 volts when it was hot. I'm exchanging it today. I'll let you know what happens. It needed the plug wires and the IAC anyway, and it's running really smoothly now.

This could easily be a grounding problem. If the alternator hasn't been checked, do that- the 10.5-11VDC tells me that either the voltage is low, the cables aren't conducting well (bad terminals) or maybe the bridge rectifier in the alternator is allowing hte battery to discharge. This can also happen when the battery cables and posts are dirty/corroded, but look fine. Measure the voltage at the battery posts/terminals, then at the cable ends. If you see any difference, address the cause. If you see no difference, move farther down the cables to the next terminal, one cable at a time.

[blackcreek]

Slow starter speed on my 97 LT-1 was fixed by replacing the terminals on the battery cables. There was corrosion back around an inch or so on all four ends.