I own a 1990 Mark VII. When I start it, it surges between 700-1800 approx RPM's. It just started to do this recently. After doing a few searches on this forum, I have come up with the IAC and PVC and screen. Can anyone please confirm this. Also, some pics of where this stuff is located would help also. I am an old carb mechanic and I can't find the PVC valve anywhere!! Thanks in advance for your help fellas.

Hello, i have a 1989 mark vii and yes i have the surging too. I replaced the EGR but the old one looked brand new and it didnt change a thing. I havent heard about the IAC i should look into that.

The PCV... I looked and looked and i finally found it Its right in the very back of the engine. Right behind the plentum (the cover, i believe thats the right word) right next to the firewall. IF you have a small hand you might be able to grab it. I ended up having to take off the top cover of the engine to get to it. While i was at it i cleaned out everything. Its a tough one.

Hope that helps some what! -Tyler

PCV: http://markvii.homestead.com/pcv.html

Try taking the IAC off and cleaning it with carb cleaner. You can also try cleaning the EVR filter, as well as checking the TPS voltage.

EVR filter: http://markvii.homestead.com/egrf.html

PCV: http://markvii.homestead.com/pcv.html

Try taking the IAC off and cleaning it with carb cleaner. You can also try cleaning the EVR filter, as well as checking the TPS voltage.

EVR filter: http://markvii.homestead.com/egrf.html

Thanks for the help. You guys ROCK!!:yourock:

OK, here is the results thus far. Took off the IAC to clean it, and it was spotless. Perfectly clean and the plunger was moving freely. Then, I cleaned out the EGR filter. It had some dirt in it, but nothing that would lead me to believe it was causing the problems. Next came the TPS. Voltage read .93 and I adjusted it to .98. I still have the problem. Tomorrow I am going to try and tackle the PVC and screen. If you have anymore thoughts, please let me know. Thanks.

Might check for a broken or disconnected vaccume line...

Might check for a broken or disconnected vaccume line...

Yup. That was my next response. Check all the vacuum lines and see if there are any cracked or anything..

Sorry guys, I should have stated that I checked the hoses already. The vacuum hoses are all correct, connected, and still very much pliable and tight. I'm going to check the PCV and EGR today and get back with ya. Thanks again.

OK,

IAC checked, cleaned and operational.
EGR checked, cleaned and operational.
EGR filter checked and cleaned.
PCV valve, breather filter, and grommet replaced with new parts.
TPS voltage reset from .93 to .98.
All vacuum hoses checked for cracks and or leaks, missing, ect.
Hair pulled out.
Two barley pops drank as a result.

I disconnected the battery to reset the computer. I tried to drive it to get it to throw a code or the check engine light and nothing thus far. All I get when I pull codes is 11's. I am very much open to suggestions.:( :confused:

When my T-Bird's TPS died, I could set the voltage perfectly, but it would still intermittently act up. So that could still be questionable. Also, have you cleaned the throttle body? What about the MAF sensor (if it has one.. I forget when the Mark started using them)?

I'd suggest checking the base idle speed next. To do that you need to get the engine fully warmed up, shut it off, unplug the IAC, then restart the car. I don't know what the idle speed is for a 5.0, but it shouldn't be too hard to find. If it's out of range, adjust it with the set screw on the throttle body. Be careful, even 1/4 turn can make a big difference!

If that's good, check the ignition timing. It should be 10 degrees BTDC with the SPOUT plug disconnected.

Ran codes today. KOER------>41 and 91
41 is supposed to mean NO HEGO LEAN RT. SIDE
91 is supposed to mean HEGO INDICATES LEAN LFT. SIDE


So, is there a way to check fuel pressure to see if I have a bad pump, OR are my o2 sensors toast?

OK, changed fuel filter, even though I just changed it about three months ago. Ya never know. I can hear the pump whining at idle. Is that probably the problem? Thanks again for the help!!

Anyone:confused: :Bang :Bang

Where is the shrader valve located so that I can check the fuel pressure. Either I am blind or it is hidden very well. If someone could show a pic, that would be better.

Right behind the alternator. Or there's one next to the fuel pressure regulator.

As bad as it was idling, it was carrying between 30-40 psi of pressure. With the vacuum line off of the pressure regulator, it would carry a constant 42-44psi. I don't think it's the pump.

Nope, doesn't sound like it would be.

Have a look at the "salt and pepper" shakers between the EGR spacer and upper intake. Make sure they're connected correctly and the pins inside haven't spread.

Someone told me MAP sensor. Does a Mark VII have a MAP sensor? What does it do? Thanks so far for the help guys.

Well, if the vacuum line came off the MAP the car would idle like it had a big cam in it and would run rich.

It's on the firewall behind the intake and looks exactly like this:

http://www.stangnet.com/tech/maf/vacuum.jpg

Wait till you hear this!!! I unplugged the vacuum line off of the MAP sensor and it runs infinately better. It doesn't idle funny, miss, or anything. That is, of course, sealing off the loose line also. When I plug the line back in, it runs like crappity crap again. I think thats my problem. Is there anyway to double check my findings, or is common sense obvious here??!!!

After a little more thinking, I changed the MAP. It runs great now. I just need to reset the timing again and I think the car will once again be perfect!!!

Awesome. Good work.

Just curious, but why do you need to reset the timing? It shouldn't have moved if it ran fine before the bad MAP.

Before I checked the MAP, I had a thought about the timing chain stretching and moving my timing a tad. So for giggles, I moved the timing to see how the engine would react, with the SPOUT unplugged of course. It made no difference which led me to believe I had another problem. It actually ran great today and I don't think I am going to re-adjust the timing.

I'm happy you found your problem! It went on for a while i've been reading the post on here! Nothing more satisfying then fixing a problem! Good luck in the future!

Before I checked the MAP, I had a thought about the timing chain stretching and moving my timing a tad. So for giggles, I moved the timing to see how the engine would react, with the SPOUT unplugged of course. It made no difference which led me to believe I had another problem. It actually ran great today and I don't think I am going to re-adjust the timing.

Gotcha. Glad ya got it fixed.:cool:

Glad you found it. I've been on more than one of those 2 week fixes and know how it feels to get it going again! FYI, I've had a bad MAP sensor keep the car from starting even after being told by numerous people that it would not. Now I keep a spare to change out while troubleshooting problems, and try to pick up extras at the junkyard when I'm there. Some parts are easier to switch and try rather than troubleshoot.
Dave.