We only have a 1999 mercury grand marquis that runs really bad in the cold. The intake manifold broke (ford recalled them and replaced many not mine) and I replaced it with a Dorman which I learned don't fit exact and will leak. I broke a bolt and obviously that ads to the leak issue. Ford has the replacement on back order nationwide and don't know a suitable aftermarket especially since Dorman is the most expensive one and leaks. Anyway im blabing. My question is if I crack open the trottle plate and wrap tape or stick cardboard or something on the lever that opens the plate to keep it slightly open will that stop the "vaccum leak" ? At least temporarily to get through winter? It idles like crap and misses like crazy but when giving it gas it runs better. So is rigging the throttle to have it cracked open a bit drawing air through airbox ok for now? It wont overheat it doesn't even reach temp. I know gas will be burned. Thanks
Even an intake manifold which isn't torqued down evenly will leak vacuum. You have a broken bolt so it's going to leak.
What you're proposing won't fix the vacuum leak. You've noticed that vacuum leaks have less of an affect on an engine at higher RPMs (higher intake airflow being measured by the Mass Airflow Sensor) than on an engine at lower RPMs (lower intake airflow being measured by the Mass Airflow Sensor).
So when stopped you're probably holding down the brake as you press the accelerator pedal. (I doubt your transmission likes that too much).
But adjusting the idle stop on the throttle body is a terrible idea and you should never do it. It's bad for the transmission. It's bad for the engine. It's bad for your safety and the safety of the drivers around you. It should never be done.
OK here's how to do it.
There's a throttle linkage idle set screw on the throttle body. It doesn't have a hex head or even a slotted end for a screwdriver because you aren't supposed to mess with it. It's "Loctited" in place. You'd have to use a small vice grip plier and turn that screw to hold the throttle plate open more.
And of course you also have to consider what your engine computer is going to think about this. It expects a certain voltage value from the throttle position sensor when the throttle plate is at the idle position. It's going to see a higher voltage value and it will probably set a code.
The computer doesn't mess around when it comes to Throttle Control. It may put the engine in "reduced power" or "Limp mode".
Maybe consider removing that broken intake manifold bolt and replacing it and then torquing down the intake manifold bolts to spec instead of creating new problems.
great review
I'm with @jack62, don't mess with that set screw. Fix the problem, don't make it worse. Don't mess with the throttle at all, raising the RPMs at idle and messing with the shifter will eventually destroy your torque converter, transmission clutches and bands. That thing isn't like an old school carbureted engine and transmission where RPMs were set with a flathead screwdriver and a timing light. Those had some error tolerances built into them, just by the nature of old powertrains
Here's Scotty explaining how to set a carb up. https://youtu.be/ZedF7QsnYag he doesn't use any of what's recommended to do the adjusting, as far as timing lights and such. He does it by ear, engineers back in the day knew things like this would be done to "approximate" settings, they made their devices accordingly.
Anyways, modern, computerized cars have almost nothing in common with a mechanically carbureted engine, they're designed for precisely maintained operating conditions -they're maintained and monitored by computer, not mechanically.
Replace the bolt, torque the manifold you have in the correct sequence and to the correct torque specification. I noticed on RockAuto that Dorman makes a specific intake manifold gasket that must be used if you put in their manifold -did you use that? If not, that's a big culprit for your problem.
Another option is getting a junkyard intake manifold from LKQ or other yard that will 90-day warranty your parts. There may be cars in there that have had their intake manifolds replaced.
Don't rev your engine and hold your foot on the brake while in gear. You will eventually destroy the transmission. Shift it into neutral if you must hold the throttle slightly open. Then release it and shift it into gear when you're ready to go. Your transmission will be thankful.
