Here we go again! I have a 91 740 wagon non-turbo and I have a miss at idle. The guy that had it before me replaced the plugs and wires, but didn't replace the cap and rotor. I just removed the old cap and rotor, which were both roasted, and put in a new Borg-Warner cap and rotor. Although there was a SLIGHT improvement in the idle miss, there is still a very pronounced idle miss. Also, when I let off the throttle or idle after the car is warm I get a popping noise in the exhaust like the engine is backfiring, but the car doesn't stall or have any no-start issues or extended crank. When the vehicle is in park or neutral it seems to miss SLIGHTLY less, but if I'm stopped in R or D it will sputter and miss even worse. When the engine is warm it seems to sputter more in N or P than in D, BUT when put in N or P when the engine is warm it will idle at around 1200 RPMs.

Any ideas of where to start looking on this thing?

 

Check for air leaks. They are a serious problem with these cars. Never can plug enough of them.

 

Are the 2.3s notorious for having bad intake gaskets/vacuum lines and such? I can understand why auto makers went away from soft/hard vacuum lines and went to electronic controls... There's a nipple in the air intake hose about halfway between the MAF and the TB with nothing going to it. I tried poking something in there, but it didn't seem to be open.

I guess I'll have to bust out the carb cleaner and start spraying down!

 

Yup. They suck. (literally) Im glad manufacturers went to electric. Theres a lot of tricks you can use to find leaks. One being using carb cleaner like you said. Another would be to take hoses off the intake manifold, plug the nipple with your finger and see if it idles better.

I just dealt with a intake manifold gasket leak on mine. Found it by listening through a plastic piece of tubing.

 

So, I got ambitious today after work and, although I wasn't able to bring home any carb or brake cleaner, I did have some starting fluid at home and I sprayed the intake manifold right on the #1 cyl on the front of the car while it was running and it sputtered a little. I sprayed it again to double check that it was for sure the intake manifold and it definitely coughed when I sprayed the intake manifold by the gasket. SO, I guess it's time to swap out the intake manifold gasket.
So is there anything special with this intake or is it just like any other intake manifold I've done..pretty much just like the big ford 6 I put gaskets in, but there's only one intake manifold. I'm guessing that the intake isn't jacketed for coolant, and I just un-bolt and clean it up. Is there anything else I should do while I have it off? I've heard that there is some pcv system, or "flame trap" to clean out or replace, but I have no idea what to look for.

I also noticed that there was a little gas in the oil, I wonder if that has anything to do with my intake leak or what I should look for next after I do the gasket, like a bad injector or something?

 

I guess I would do a simple compression test and see what the results are. It should only take about a 1/2 hr to do it and if all cylinders are about the same then consider pulling and replacing the intake.

 

What does the compression have to do with an intake leak? I'm going to change the intake manifold gasket, flame trap hose and nipple, clean it all up good, drop the gassy oil out of the pan and get some fresh oil in it, and go from there.

 

A miss can be caused by a burnt valve. It is easy to check and may save you some time. I have 310K miles on my 89 740 and have never experienced a vacuum leak. Other then normal oil changes and timing belt changes I haven't replaced any vacuum hoses. Also the same with MAF and other sensor. I have done a few exhaust systems and recently did the fuel pumps and relays. Car idles at 700 RPM and runs up the rev range without a miss. I usually don't pull things apart until I do a few basic test like compression and leak down. !st is reading and solving the codes then the tests.

 

Well, it runs like a champ! I don't know what kind of drugs the kid I bought it from was on, but I'd like to get some...he kept telling me, INSISTING that the transmission mount was what was causing the "shake" at idle...boy was he wrong!
The gasket on the lower half of the #1 cylinder was missing about 1" of the gasket, which was STILL ATTACHED, but fell off when I pulled the manifold away from the head. There were 2 splits in that 1" that had been leaking for some time as they had carbon built up on them pretty thick. I replaced the whole flame trap and hose, minus the box, and the line that went from the trap to the intake. I also decided to splurge the 10$ and buy a new set of plugs, and I was right to do that too! The plugs I took out weren't even gapped, and I could barely get them over the .020 of my gapper. I gapped the new plugs between .028-.030 and put anti-seize on the threads. Then I changed the random oil that was in it and put in some fresh 10w30 and a little lucas. When I went to fire it up it hesitated a little from all of the carb cleaner I used to clean out the ports in the intake and the head, but after the struggle it fired right up, and drove great!

I don't know if this is important, but I put a light coat of some of my Motorcraft engine sealant on the gasket I had left over from when I was wrenching at Ford. I hope that helps it seal up a little better.

Because of the one nut on the #3 lower the intake was a solid 3.5/10 for difficulty.

 

OK great so the miss is gone. Sounds like someone was in there before you. So what was the vacuum reading before and after at idle. It must be up to 17-20" . Enjoy the ride.

 

I wish I had a vacuum gauge...i've never needed one. All of the leaks i've dealt with have responded well to brake or carb cleaner. I didn't need an actual vacuum reading, but if I was stumped I would buy one asap.

On the upside I found out that I have girling calipers in the front...before I went out and bought brake pads.

On to the ses light and the srs light after that.