Vaccum Test at steady 4 Hg. Can Bad ICV cause bouncing idle and loss of vaccum??

[Grasshopper2Ant]

Have a bouncing idle. 300 rpm to 1100 rpm up and down continuously. When I stomp the throttle it would hesitate or stall.

Took a vaccum gauge and I have low vaccum at 4 Hg instead of 17-22.

Would a bad ICV cause a steady low vaccum?

I have propane and carb cleaner tested and found nothing obvious for such a big loss in vaccum.

I have already took original ICV out and replaced with a used one off 1991. I cleaned it, ohm tested it to spec. and installed and problem persists.

In the process of getting a new ICV but want your opinion if a bad ICV can cause my issues before I order it.

[Eric93se]

You vacuum leak can also be at the valve cover gasket and oil cap. But you should make a smoke tester, I made this simple one and it worked well. Just can't do it on a windy day.

https://www.youtube.com/watch?v=GAqHqKq09CA

[Grasshopper2Ant]

Thanks Eric93se, I also saw a transfer pump / cigar method that may save me some time.

My loss of vaccum is severe so I thought it should be obvious.

My resistance reading for 92 "silver" Bosch ICV: 1/2: 13.1 ohms / 2/3 : 12 ohms / 1/3 : 23.8 ohms. All within Bosch specs.
My resistance reading for 91 "black" Bosch ICV 1/2: 22.7 ohms / 2/3 : 21 ohms / 1/3 : 42.3 ohms. All within Bentley specs.

The silver ICV used to click clack but now the flap moves silently back and forth.

Another clue is I can hear/feel the vaccum sucking on the u tube to manifold. The u tube connections are tight.

Given the above info, can the ICV be the cause??

[Eric93se]

Not likely an IACV issue.

[tjm3]

Check the gauge and the attachment point to the intake manifold.

[Grasshopper2Ant]

Update:
Took vaccum test initally at small vaccum tube off valve cover.... 4 Hg steady.


Took vaccum test off brake booster …. 8 - 21 Hg bouncing.


Intake manifold, faulty injector or head gasket ??


** Forgot to mention intentionally as I thought it was a separate issue. I am losing water in the rad internally ( verified by rad pressure test). I can see it in the exhaust pipes. **


Where do I go from here ??

[tjm3]

The hose going to the valve cover doesn't provide manifold vacuum.

Tapping into the brake booster vacuum is a good way and the bouncing from 8-21 InHg could be several things but usually points toward some valve problem, bad valve spring, leaky or burn valve, flat cam lobe. Needs further diagnosis. In any case, the bouncing points to one or more cylinders not doing its job.

Some water coming out the tailpipe is normal, especially if the cat is working properly. If it's coolant colored, well, that's another issue.

[Eric93se]

Probably going to have to source a new/rebuilt head.

Start with a compression test then a visual inspection with the valve cover off.

[Grasshopper2Ant]

I never used a vaccum gauge before. It has given me good info from the reading as I do not have a OBD 1 reader.

I am going to do a compression test wet/dry to get more data to analyze.

Car runs fine if you can feather the throttle to get past 1000 rpms.

I am losing more water than normal through tailpipe. It is clear color as far as I could see but I have been topping up with 1/2 litre every few days.

Main question : Can internal head gasket coolant leak through the exhaust valve cause bouncing vaccum and idle ?? What compression readings will reveal internal coolant leak ??

I was hoping for a easy vaccum leak but am prepared for the worst, a head gasket!!

[tjm3]

The vacuum gauge is a good tool for some stuff, but not coolant leaks. It's a dynamic tool and measures the (air) pumping action of the engine. A coolant leak may enhance or mask a vacuum reading, but either way some other test needs to be done, and you're guessing. A compression test may tell you the head needs to be removed, but not necessarily why, and it's probably still a guess. A leak-down test will give you an indication of where the problem is, but the head still needs to come off, better data and still an educated guess but a more narrow one. Once it's off (the head), a plain 'ole visual inspection should pinpoint the problem (head gasket, warp, crack, etc). If you're losing coolant and it's not on the ground under the engine then it can only go two places - in the crankcase or out the tailpipe in one form or another. And the head still needs to come off.

[Eric93se]

You shouldn't tell him that its a simple visual inspection for warpage or cracks, both require either a tool or experience.

- - - Updated - - -

You really shouldn't drive the car either. A lot of people probably don't realize it but the crank arm can bend from having water in the cylinder. One would have to check that all pistons come up to the same height when the head is off.

[tjm3]

OP, you've gone from a vacuum leak to water filled cylinders and bent rods with no real diagnosis in sight.

Good luck to ya'!

[Grasshopper2Ant]

My dilemma is the coolant loss related to the bouncing vaccum.

I am losing the coolant through the tailpipe which I probably can live with for now. No milkshake in CC and no oil in coolant.

If I can solve both problems, I am more inclined to do the head gasket, not just fix coolant and have a bouncing vaccum / idle.

Took compression reading 90 - 95 dry / 95 - 107 wet …. does not seem out of range.

I may do a smoke test and maybe a leakdown test and go from there.

[Eric93se]

These engines don't make milkshakes and don't typically have a HG failure, what does happen is the heads warp and crack.

If your engine was fully cold then your readings are probably fine, on the other hand if the engine hand been running earlier then the reading are not good.

- - - Updated - - -

Shine a light down the cylinder and check for any shinny piston tops, that would indicate that it has been steam cleaned.

[XnWarden]

Lol at this whole thread. You have low vacuum AND low compression. Better just start a turbo build while you're in there

Sent from my SM-G975U using Tapatalk

[Eric93se]

Cold engine typically around ~120, warmed up engine ~160.