Problem with idle (or lack thereof).

[Klickmania]

Maybe you guys here can help me. I just rebuilt my 5.0 out of my '92 GT over the past two months, and now I'm having trouble getting the thing to idle. Here's a little background on the car though. For WHATEVER reason, the previous owner put a 5.0 out of a '71 Torino or Fairlane in the car, with the '92 fuel injection. The engine had been rebuilt, rather poorly I might add, I think in '08. It's bored .030" over, and the crank is ground down for .030" oversized bearings. Obviously the cam wasn't a roller, but I decided to do a roller convertion with an f-303 cam and lifter package and the correct length pushrods from Edelbrock. I have the timing set for 10* BTDC with the spout out, and I've quadruple checked the firing order. Everything on that end seems to be in order.

Anyway, the car will start (you do have to mess with the gas pedal a good bit to get it to do so) but it won't run under about 1000 rpms. I hooked up my vacuum gauge to the manifold, and nothing even registers under 1k. Once I get up to 1500 rpms and above, I'll have around 15-17psi when I let off the gas. It runs like a champ above 1500 rpms too. I have seen the surging idle check list that's floating around here, but that seems to be for a slightly different problem then what I'm having since I can't get it to run without playing with the gas. I've also checked for vacuum leaks probably 5 seperate times now. Do i need to reset the throttle plate in the throttle body and the TPS? Or should it atleast idle some, without any fine tuning? Not sure exactly what to do. Hopefully you guys can help. I look forward to any replys, I definitely appreciate it.

- Spencer

 

[Lawbreaker5.0]

I had to mess with the TB screw to get mine to idle on the initial first start. I had to remote start it while turning the distributer and messing with the throttle underneath the TB. I finally got it to idle. Then held it there while I unscrewed/screwed the the adjuster bolt. This was a used bbk TB.


Edit: How did you set timing if the car won't idle?

 

[Klickmania]

Thanks for the reply man. Definitely appreciate it.

You can set the base timing before you start the car. Just have to make sure number 1 piston is at TDC on the compression stroke, the timing mark is at 10* BTDC, and the rotor in the distributor lines up with the number one plug wire. It's just a rough estimate right now, really. I know I have to fine tune the timing once I get this idle problem fixed. I guess I'll try and mess with it some more tomorrow after work if it's not raining.

Is there any specific method to getting the throttle body blade adjusted, other then unplugging the IAC motor, and moving the screw on the bottom of the throttle body? Then starting it up. I'll definitely check before I pick up my tools. Do you just open it up until it idles where you want it?

Ford Mustang Base Idle Reset

I'd basically do that, correct?

- Spencer

 

[Lawbreaker5.0]

Oh, saying with spout out through me off. Just open the butterfly up by holding the lever underneath the TB, then turn the screw to where your holding it (listening to the engine). I set mine intially at right at 1k. then I let her warm up and set the timing. Then did the base idle reset and adjusted the TPS.

There could be a better procedure and someone will chime in to correct, but this worked for me.

 

[Cobra1741]

yea.. get that tps around .98v. and maybe look at your Fuel pressure regulator?? see what psi your running at. should be 38-40. is there any kind of tune on the computer or anything??

 

[HISSIN50]

Is the IAC functioning properly?

 

[jrichker]

The no run and low vacuum at 1500 RPM suggest a vacuum leak or misajusted valves. I have seen several instances of where the intake manifold gaskets slide out of place on installation, creating a leak that is very hard to find.

See http://www.stangnet.com/mustang-forums/795959-high-rpm-control-computer-2.html#post8246006 for the same problem & pictures of the slipped gasket.

Michael Yount’s valve adjustment proceedure

Here's an easy way to determine this. Start with the #1 cylinder. Rotate the engine with a ratchet on the crank bolt clockwise. Watch the #1 pushrods. First the exhaust pushrod will rise and fall signaling what would be the exhaust valve opening and closing if the rocker were on. As it closes the intake pushrod will rise -- keep rotating clockwise until the intake pushrod falls and is level with the exhaust pushrod - both at the same height. Both lifters are now on the base circle of the cam - both valves would be closed if the rockers were on.

Now, install both rockers. Tighten the bolts with one hand while rocking the rocker with the other hand - continue until you reach the point where you can't 'rock' the rocker any more because there's no gap on the valve stem end or the pushrod end. You are at zero lash - i.e. - no gaps. Stop tightening just as you reach this point.

Now, put your torque wrench on the bolt and tighten it to 18-20 ft-lbs while counting the number of turns it takes to reach the torque. You should hit the torque within 1/4 to 1 turn of the bolt. If it takes more than 1 turn, use a shim to raise the rocker -- each .030" shim will reduce the number of turns to torque by about 1/4 turn. If you reach the torque in less than a 1/4 turn, or you have trouble reaching zero lash even at full torque, then you'll either need longer pushrods, or to CAREFULLY remove some material from the bottom of the rocker fulcrum. Using the procedure described above, you will work through the remaining 7 pairs of rockers. If you follow the firing order, it will minimize the manual cranking you have to do to get the lifters on the base circle of the cam prior to installation of the next pair.

When I first went through mine, 13 of them took no shims; 3 of them took 1 .030" shim. Upon cranking it up, one or two of them sounded a bit noisier than I thought was right, so with the engine hot, I pulled the upper off, and the valve covers, and went through the installation procedure again. That time, 11 of them took no shims; 4 of them took one .030", and one of them took 1 .060" shim. And they were very quiet running.

Good luck with it.
__________________
Michael Yount - K'ville,TN 82 Volvo 242w/5.0L; 2000 Suzuki Bandit 1200

 

[Klickmania]

Thanks for all the replys guys! I guess I'll do these in order from simpelest to hardest. I'll start by trying to reset the throttle plate, if by some miracle that's the only problem, but I doubt it. Then I'll check the valve adjustment. If that doesn't fix it, I'll check the lower intake gaskets. Now, I didn't put any silicone on those since they had a rubber strip molded in. The gasket set didn't say anything about it in the instructions. Every other place I checked online said something different about it. Some places said to use it, some said not to, so I just took a chance. We'll see, and I'll definitely keep you guys updated.

Would a leakdown or compression test help determine if the valves need to be adjusted?

I'll also see about getting a fuel pressure gauge this weekend.

Also, where can I get those shims for the rockers? Keep in mind they're off of a '71 302, not a '92. I dunno if that makes any difference.

- Spencer