87 S4. It starts up strong then dies right away after intake refresh. Seems like a MAF problem. It worked fine before removal. The car will idle on its own with MAF unplugged so I have ruled out any timing, spark or fuel issues. Any ideas other than MAF failure?

 

Whether it might have been the vaccum leak I found or maybe the MAF just started working I do not know but the car is running now. It is raining so I will need to wait till Fri. to really test it but it sounds good. The vaccum leak was the line that goes under the water bridge back under the intake. The hose was completely off. I got it back on but there is no way to tighen the clamp. If everthing works well I might take it back on in a few days and see if I can smear a small coat of gasket maker on it and then slide the hose back on.

 

I guess nothing got fixed. It seems like there is unmetered air getting in and making the car run like ****. It will not idle without stalling and stumbles at lower rpms. I have checked all injector connections and plug wires. It seems to get stronger with more gas so I am ruling out fueling issues. I did nothing with the front end to mess with timing. I think I do hear it sucking air at low rpm so maybe there is a massive vaccum leak. I guess now I need to just lift the intake back up and see if anything is unhooked.

 

You can make up an intake sealing tester out of plumbing parts, like the one pictured below. Then you pressurize to 2-3 psi and listen for leaks.

Here's Dwayne's instructions for making one:

https://rennlist.com/forums/6188035-post4.html

 

One place that can be a culprit is the ISV and its hoses. Check the clamps on those and make sure they are tight. Loose one can also cause the ISV to not operate since the LH may think more air is going in. This was one of my issues until I replaced a clamp with a better one.

 

I have been thinking about building one of those but I think my leak is obvious and massive. I really am starting to think one of the isv boot hoses might be completely off. I just feel like it is getting a lot of unmetered air. I covered the intake with my hand and it has almost no effect on the engine untill I get to a high rpm. I am sure I need to take the intake back up and see what I missed.

 

Took intake back off and found that the isv feed tube was completely unhooked. In the back of my mind I was thinking I screwed up on that and now it is comfirmed. That would obviously let a mass amout of unmetered air in. Going back on now and hope it runs normal in a few hours.

 

I had the longer ISV hose split on me after the intake refresh, the hose was new!

Sean down in Tx had at least one same issue.

On my car the ISV hoses were not clamped at both ends from the factory........they are now.

 

Back to normal and even better. It started right up at about 1000 rpm and quickly settled down to about 900. I know its suppose to be about 800 right away but maybe after I run the car a little it will be fine. It is a far cry better than the 1200 to 1400 I used to start at for the first 5 minutes before I finally settled in at 800 or 900.

 

Pleased i found this thread. This is exactly the same symptoms as my car, being a novice working on a 928 what bits do i need to take off to get the intake off, do i need to remove the rails either side completely or is there enough room to just undo and flex them???

 

You need to read (and/or print out and make a manual) this thread by Dwayne. Read it several times first. It is truely a masterpiece on the Intake.

https://rennlist.com/forums/showthre...ferrerid=75372

 

Yup exactly same deal on my car, hose blown off!

 

Yep, follow Dwaynes instructions closely and you will be fine. Just make sure nothing falls into the engine with the intake off. I am sure you don't need to ask me how I know. Just be very carefull and plug the engine with rags as soon as intake is lifted off. Also a good idea to take a magnet and flashlight and snoop around a little just to be sure nothing small has fallen in any of the ports before install.

 

Idle speed will be higher cold than hot, say 1000rpm when cold then gradually falling to the "normal" 675rpm for S4.

Any false air in the intake/plenum etc will be measured by the MAF which will then make the car run much too rich. Unplugging the MAF will make the car idle reasonably well. This is because the LH recognises there is no MAF volts and uses a preset injector pulse width (limp home mode).

But sometimes because the engine runs "better" with the MAF unplugged it is thought that the problem could be the MAF, when it isn't. The true test would be to check manifold vacuum with the MAF unplugged, that would soon indicate if the problem is a vac leak or not.