I just checked my MPS because my car is running rich, burns a lot of fuel, and idles very poorly especially when warm. The CHT was bad and I replaced that. IT improved the stalling I had before replacing it, but the car is still rich and idles very unpredictably. I put 15mm Hg on the MPS and it lost about 1/2 mm in the first minute and 4-5mm within 5 minutes. Would that be considered a bad MPS. If so does anyone have experinece with rebuilt units from AA or Preformance Products. AA is about $40 cheaper. Thanks for any input.

You can send it to Bleyseng here on the board. He will likely chime in here if he sees this post, but you can PM him using his screen name for a quicker response.

I wouldn't consider that unacceptable, but that doesn't mean it's good. There are ways for it to break that will still allow it to hold a vacuum. The only way to know for sure is to take it apart, or test it with fancy equipment. A quick and easy test is to borrow a known good MPS and see if it fixes your problem.

That is a very slow leak. A leak that slow will not cause any change in performance and is definitely not the cause of your car running rich.

I thought that that may not be a fast enough leak, but I was not sure if it had to hold a constant vacuum to function properly. I was actually hoping that was enough to cause a problem, becasue it would be an answer, everything else seems to check out fine

ok, did it run fine before?

Do the numbers for the ECU and MPS match? tell us in detail about your engine/FI with the numbers on the ECU, MPS, CHT etc.

The vacuum numbers sound ok to me so I think your rich problem lies elsewhere....

Temp #1 sensor still plugged in?
Fuel pressure ok and at 29-30lbs. Too high (50lbs+) means the return line are kinked

give us more to work with here....can I buy a vowel???

Being a recent Bleyseng customer that is having the same problem, I'm going to chime in. I doubt that 8 in. Hg in one minute is causing that bad of a problem. I pumped my old MPS up to 20 in. Hg and it leaked all the way down within a minute. The MPS was obviously bad, so I replaced it and the car ran only a TINY bit better. It will idle without flooding out now(which it wouldn't do before), but it's still SUPER rich. There's still other problems to be resolved.
So before spending the 200 bucks, I would check what I've since found out is the problem with my car. T in a vacuum gauge to your line going to the MPS and see what kind of manifold vacuum you're pulling at an idle. I think it should be around 20ish. If it's lower than that it means two things. A: you have a vacuum leak somewhere between your throttle body and the heads(or maybe in the hose itself), and B: your MPS is getting a false reading to meter the fuel by. You can also manually pump the MPS up to about 20 in. Hg and see how it idles (which may be a bit more difficult if it's leaking down). Make sure to plug the loose MPS vacuum hose when you do this. If it runs well, this should eliminate any electrical fault between the MPS and the ECU as well as a fault with the ECU as well. Of course, all of this is assuming proper fuel pressure. Check that first. I'll shut up now.
Mark D

You should have about 15hg at idle with a steady needle on the gauge.

if you don't check your compression with a tester
check for vacuum leaks
check for the timing being off with a timing lite
check the valve adjustment!

the engine must first be in a good state of tune to start to even figure out what is going on with the FI. Then half the time after all the other issues are fixed the "FI problem" goes away.

okay here is some more information. The valves were adjusted about 500 miles ago as well as the timing checked and the dwell set. I tested the temp sensor at the throttle body and it gave the correct numbers. The CHT I replaced because the wire going into it was having issues and when it moved slightly the car would stall. Now it does not stall. When I first start the car it dies and will immediately restart and stay running. Sometimes if I try to move it right away it will pop back a little if I do not give it a lot of gas. after a minute or two of running there is no problem with that. There are times when it will idle rock steady, but if I push the pedal down at all when it is idling well it will immediately start to go up and down on idel from almost 0 to about 1000 rpm. When I pull up to a stop the car drops idle for a moment to almost a stall and catches and is okay but idle wanders. I can smell it running rich and it is only getting about 21-23 mpg. I will check the ECU and MPS to see if the numbers match but from what I know of the car they are original to the car. Th engine only has 44K original miles and not much was done to it over the years. I have replaced all of the vacuum lines and fuel lines except the ones in the tunnel because they were amazingly good. The fuel pressure is about 30-31 lb. The car has plenty of power when driving and no hesitation at any point in the full RPM range after idle.

1. change out the points to a Crane optical points replacement. Electronic ignition is a big help.
2. Set the idle mix when the engine is hot, after 15 mins of driving, AAR valve is closed.
Use a CO meter if you can get one, go to a shop etc.....or
pull over after the car is hot and reset the idle ECU screw to where the engine idles good and reset the idle speed to 950. Do it a couple of times. The idle knob on the ECU should be close to the factory notch.

It sounds like the idle mix is rich a bit. Make damn sure the vacuum hoses are setup correctly.

Bleyseng, thanks for the reply. I actually think the mixture on the ECU may be wrong. Before buying the car I knew nothing about these cars other than Iwanted one since i was 10 years old. The previous owner told me there was an adjustment for summer and winter and he had adjusted it. IT sounded a little fishy to me, but in January when I bought it, it was running well accept an occasional minor idle issue which I had seen in many 914's I looked at, now that the weather here on Long Island is 80 degrees verses 40 degrees I have problems. I am going to look into that, because I can't find any vacuum leaks and I was careful with the vacuum hose routing. Thanks.

You should drive out to Movie Time Cars on the 26th over in Jersy so the guys can have a looksee at your car. I may be there and if so can help.

Look for the thread titled North East Wrenching revisited or something close to that.

I would love to go to the wrenching day and get some input, but I have to work. I did try adjusting the ECU and did get some results, but they would say to me there is something more going on. In order to get the car to idle smooth, I have to have the knob on the ECU turned all the way counter clockwise and then adjust the air screw on the throttle body so it idles down a little below 1000 on the tach. Then it idles real smooth. If I hit the gas and release it, the idle bounces up and down minorly 2-3 times and then idles rock steady again. I don't think I should have to completely lean out the ECU to get that sort of idle and the car still smells a little rich, but not as bad. any more suggestions. How do you guys suggest checking for vacuum leaks, I have checked to see all lines are connected tightly and in the right place. How do I check and see if it is leaking vacuum in places like where the throttle body attaches.

Ok, I have re-read everything and have no idea what model car you are talking about.
You don't have a signature line either so I am lost.

Tell us the year and model, engine size and the ECU, MPS numbers or I am gonna get out the Great Swami to do a reading......


Need more data to do a Transamerica Shadetree repair.

Sorry I missed somehow putting that information in. It is a 1976 2.0 with completely stock fuel injection. I will get the numbers off the ECU and MPS shortly now that it is daylight and I can see them. I usually put that info in when I am posting I don't know how I missed it. Sorry.

okay the number on the MPS is 0280100042. The ECU has two numbers. 0280000052 and 039906021A with the VW symbol next to the later number.