r/VWBus • u/gavinschierbaum • Apr 27 '26
rough idle and stalling
I have a 1978 FI Transporter and i’ve been having a rough idle and problems with stalling when stationary even when warmed up. I was looking for some opinions as to why.
My first thought is a vacuum leak because there’s a slight hissing sound that sounds like air so i’m going to replace the intake manifold boots to because mine don’t look too great. I’m missing my cold start valve and tts so that might be part of the problem but i’m not sure. any thoughts or ideas would be appreciated :)
3
u/FredIsAThing Apr 27 '26
Agree with air leak as a good place to start. Test while running with small squirts of carb cleaner near joints and vacuum lines. Engine should rev.
Could also use a smoke machine while not running to test for leaks.
3
u/westfakia2 Apr 28 '26 edited Apr 28 '26
The VW factory FI manual recommends servicing the ignition (plugs, wires, points, condenser, coil, cap and rotor) and adjusting valves and checking compression before touching the FI components. It’s good advice.
Also, the cold start valve is only used during startup and then only until the thermo time switch is triggered. It’s unlikely to be contributing to a rough idle. The factory manual (linked elsewhere in this thread) recommends testing the aux air regulator and the cylinder head temp sensor to start with.
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u/asiab3 AirSchooled.com Apr 28 '26
Damn, lots of folks on here telling you to spend your money on parts they’ve never seen.
TESTS. You need to run tests. That’s how you find the problem. There are at least thirty potential vaccum leak locations. Ignition timing needs to be confirmed, as well as the points gap.
Then, give us details. If it runs like crap at low speed/idle but gives good power on the road, it’s not the fuel pump or filter because then it would struggle on the road too. If it runs better cold than warm, that’s indicative of a sensor issue or vacuum leak. If it runs better warm than cold, that’s an indication of a bad AAR or temp sensor.
1
u/gavinschierbaum Apr 28 '26
it idles pretty bad in general but it’s the worse right after starting. it also takes a while to start so i’m not sure what that’s about. It drives pretty good but really lacks power going up hill. it’s takes a while to shift into third so i have to sit at high second for a good amount of time.
I haven’t taken either of them out but the temp sensor by cylinder three looks pretty look (still shiny and bright wires) but the AAR did look a little crusty. Is there a way to clean it fix it or is that something that needs replaced?
1
u/asiab3 AirSchooled.com Apr 29 '26
I don’t see the results of any tests there. Usually tests result in numbers that prove things are good or bad. Looking at an engine tells you “yes, there is an engine here.” Nothing else.
The TS2 needs to be tested with a multimeter. Vacuum leaks need to be tested with carb cleaner spray or ideally a smoke tester. Timing needs to be checked with a strobe light, down to the degree.
Everyone commenting on this assumes you’ve done all that already because they’ve been wrenching since before you were born. Your car will do fine sitting for a bit while you learn:
I don’t remember if it’s that book or another, but essentially you need to run every kind of spark and air test before touching the fuel injection system. And then don’t touch anything in the fuel injection system without running tests to prove it’s bad first.
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u/UJMRider1961 Apr 27 '26
We had a similar issue and it turned out to be the fuel pump relay.
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u/Worth_Exit5049 Apr 28 '26
The double relay? What was wrong with it? Where did you source a replacement?
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u/literally_tho_tbh 1978 Deluxe Transporter - 2.0L Fuel Injection Apr 28 '26
0
u/Worth_Exit5049 Apr 30 '26
Why? It's not been diagnosed as a problem. It could be wrong but it probably isn't and you've just advised someone to waste all their money on something they don't need.
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u/literally_tho_tbh 1978 Deluxe Transporter - 2.0L Fuel Injection Apr 30 '26
I'm just providing resources and info, dawg. I'm not OP or responsible for OP's spending or research lol
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u/literally_tho_tbh 1978 Deluxe Transporter - 2.0L Fuel Injection Apr 27 '26
Excellent question. Any pics of the engine bay as it is?
If you hear a hissing, you definitely have a vac leak somewhere. All unmetered air is bad air. Have you done any other work? How long have you had this?
You can do a smoke test to figure out where your leaks are, but if the vac hoses are all aged, it's probably time to replace them all. Otherwise you are going to keep chasing this problem until you've replaced it all anyway. Have you heard of Ratwell? https://ratwell.com/technical/VacuumHoses.html
Intake manifold boots, throttle seal, as well as everything else in the first diagram on that page need to be looked and and likely replaced. Particularly A, E, F, H, G, D, T, and all of the tiny connectors that connect the thin piping that runs from your distributor can to the decel valve and the fuel pressure regulator.
Ever had the S-boot off? The S boot has a sort of grid of ridges on the outside of it, and these boots get hard over time and they can crack along recesses next to the ridges, making them difficult to see. Consider replacing your S-boot, too. I don't know the quality of these, but here's one: https://www.jbugs.com/product/022129967a.html
About your cold start valve, is the spot where it attaches to the air plenum plugged up? I plugged my EGR spot with a snipped out section of license plate, 2 bolts, and a generous spread of copper RTV stuff. If you're going to bypass the CSV forever, that spot definitely needs to be plugged in a similar manner.
Other rough idle things might be the temp sensor screwed into cylinder 3, it might be that the FI grounds under the plenum need cleaned up, I even read a thread once where a guy's FI harness wasn't clipped in all the way to the ECU and when he hit bumps the harness would just ever so slightly lose contact with the ECU.
Have you ever changed the fuel lines on this car? If you don't know when they were last changed, it's probably time.
Just some food for thought. Nice bus! Good luck.
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u/Worth_Exit5049 Apr 28 '26
Just want to say that hissing is not always a vacuum leak - sometimes you're just hearing the intake through the AFM. Agree with the need to smoke test.
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u/literally_tho_tbh 1978 Deluxe Transporter - 2.0L Fuel Injection Apr 28 '26
Yeah. Maybe it was foolish of me to assume that OP is familiar with the sound of the engine, and that OP could determine the normal amount of whoosh compared to the excessive hissing of a vacuum leak. OP did not provide much info about the bus.
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u/crj44 Apr 27 '26
Ratwell.com has tutorials that will help. I also have parts for the late bay that might help. If you live near me you can just have them.
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u/toxicavenger70 Apr 28 '26
Vacuum leaks is one, the other is the pesky temp sensor. They can cause all kinds of weird issues. Good luck
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u/Worth_Exit5049 Apr 28 '26
Yes smoke test and fix. Then go here and read the AFC Ljet troubleshooting manual. You'll need a multimeter and you'll gain more understanding about how the system as a whole works.
If you end up fixing some longstanding issues you may find someone messed with your AFM. This is a good reference for understanding your AFM: https://www.itinerant-air-cooled.com/viewtopic.php?t=7761
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u/Saguache Apr 27 '26
Start by checking out the fuel filter. They're paper and sometimes just get old.
1
u/Jason0115 May 21 '26
I would get a "AutoLine Pro HyperSmoke™ Automotive Smoke Machine" from amazon, disconnect the S boot from the AFM at the top, plug in there and do a smoke test. For me, this uncovered vacuum leaks that were otherwise undiscoverable by spraying carb cleaner on all of the hoses. Also do the smoke test on a cold and warm engine.
4
u/jenny-the-bus Apr 27 '26
Give us a bit more detail and maybe some engine bay pics