I am pretty sure I have a bad brake booster, (220K original booster and MC) when I bump the hose coming off of it I hear air hissing (grommet looks bad also) and when I hit the brake at idle I hear hissing.


Could this be the cause of the minor rough idle I am having and the surgeing at idle that began a week ago after installing a new computer?

Doesn`t the brake booster tie directly into the PCV valve?

Thanks.

 

The brake booster vacuum line ties directly into the intake manifold tree.

No where near the PVC valve, that ties into the air intake.

Bad brake booster, blown out diaphragm could be a major source of vacuum leak, and a major vacuum leak most offend causes high idle.

 

I dont really have high idle, it idles slightly rough but the biggest problem I am having now is this intermittent surge of the engine while I am at a stop (since I installed a reman. computer a couple weeks ago). Today driving 22 miles it did not do it at all, the last couple days it did it 3 times. I put it in Neutral when I come to a stop in case it does it, that way the van does not jerk forward. This is very tough to diagnose. This weekend I plan on checking for more vacumm leaks.

Thanks.

 

Yeah, I would think a bad booster could do this. Perhaps it's causing a variable vacuum leak that the PCM has a tough time adapting to as you're sitting at a stop. Just a WAG, but I think you're on the right track with this one.

Try capping the booster line altogether and see if the concern repeats itself. Preferably in the driveway, don't go driving around without power brakes!

 

Today on the way home from work it got worse, The idle jumped up really high while I was stopped and did not return to normal, I hit the gas but that did not help, I had to put it in neutral and shut off the engine then restart it, by that time traffic had started moving

Then it did it 2 more times. I probably shouldnt drive it but its my DD. Ill have to keep putting it in neutral when i am stopped to be safe.


I am getting 2 codes that one of which may be the culprit, 311 Thermactor system fault and Excessive converter clutch slippage.

Could the clutch slippage cause this?


I found a post that says, after installing A new computer let it idle for at least 15 minutes without touching the accelerator, Is this right?

I also found this:
I know its for a F-150 but probably the same for E series and others?



It did not do this with the old computer.


Thanks.

 

Nope, the converter clutch doesn't engage until commanded to lock up, which doesn't happen until the van starts moving. It would kill the engine if it locked at idle.

 

Ah, I see.
Yesterday I (visually, probably should hit them with some soapy water) checked all the vacuum lines from what I am pretty sure is the vacuum canister, Passenger side front fender and could not find any niticeable problems.


I let it idle for a long time and pushed the vacuum line several times back and forth on the brake booster and it hissed very loudly but the idle did not change. Grommet has dry rot.

Pressed the brakes hard and soft till I hear hissing and still no change in idle.

I am wondering how critical it is to follow those instructions when installing a new computer? Maybe I should do that because I did not do that when I installed the computer, I just plugged it in and drove it.

 

Have you checked your TPS?
Of course my Saturn is much different but it is a standard transmission and when stopped the idle would jump up to 2000 rpms sometimes. The only way to get it to reset would be to turn the key off and back on.. There were no codes...

here are a couple of videos.

 

No, because I am not getting a code related to the TPS, but.. I probably should anyway.
The surging at idle is very intermittent, On average It only happens like once every other day.

Thanks.

 

Your current problem on this thread is not the related to the TPS.

Also, the posted videos are for newer models, and Not applicable for your '90's era van, This should be the only Link to follow for that era vehicle, testing the TPS.

The more "testing" you do, like "........and pushed the vacuum line several times back and forth on the brake booster and it hissed very loudly......."

That, right there tells you there is a problem with the brake vacuum booster, which has been mentioned above, several times.

You can let it idle all day and night, and you'll get the same results, but put it under load, and the vacuum increases, and then.........you'll get the vacuum leak, and Might, result in the high idle caused by a major or minor vacuum leak.

Also.......you have several threads relating to installing a new ECU, as I have wrote in other threads, you need to get at least 50 miles on a newly installed ECU for the computer to "learn" the engine, and do it's tuning.
That you have done, yes?

One thing, which I'm sure you followed?? Did you match numbers from your OEM ECU to the re-man unit?? That is very important. There are like 5-6 diffrent ECU's for replacement for this era vehicle.

If your in Sunny CA, did you get the ECU for California Emissions ??

 

It does not have high idle all the time, just a surge very infrequently after installing new ECU.

Yes, I have drove well over 50 miles after installing it.

There were no numbers on the new one to match to my existing ECU.
I checked online and had the store confirm I was getting the correct ECU for my vehicle when I picked it up, and yes, it is a California compliant version.

 

Oreilly`s did not have the brake booster check valve or grommet so I figure Ill try something.... I purchased some good quality rtv, cleaned up the the grommet and the metal around the grommet and let it dry, applied a good amount of rtv to the grommet and around the sealing area let it cure for a day. It made a very good seal. I took it for a test drive and now it idles very quieter and smoother, so much that I can hardly tell the van is idling. But, I still hear a hissing when I press the brakes.

Does that make sense?


Today I went ahead and removed the engine cover again and I traced every vacuum line again. The hose from the booster to the vaccum tree is intact, PVC to the intake is good, all the hoses from the vacuum canister to the tree are good, from each of the solenoids and the diverter air valve for the thermactor system are good. The only lines I could not get to are the ones coming off the pump. When I say good, they are connected and no visible breaks.

 

If your still hearing the hissing sound when you apply the brakes, that still is a bad/leaking diaphragm inside the brake booster. If the diaphragm pops, you'll be back to a major vacuum leak.

Sealing up the vacuum line/grommet to the booster will/did solve the problem with the intake vacuum leak = high idle.

It's still worth the time to check/replace all the vacuum lines

The large lines from the air pump have nothing to do with intake vacuum, That's for the pollution junk. But if not connected, you'll hear a loud "blowing" air sound.

 

I started to pull off the plastic corrugated split tubing that is used over the vacuum lines, same type of stuff over electrical wring and it literally broke off in pieces so I stopped and was afraid the vacuum lines would do the same but they are probably a better quality plastic.

I plan on doing the booster and the MC at the same time when funds are available.

Thanks Wild.

 

This is just for information...
I came across this site a while back when I was making the harness for my 85 and have ordered a a couple of relays from them,, but they sell the "loom" you are talking about.. The problem is that I think they only sell it in boxes of 100'. But it will give you an idea of what is out there to use for a replacement.. Their loom is rated -49F to 300F
https://www.delcity.net/store/Split-Wire-Loom/p_800821

This company sells it by the 10' or more but it is not rated as high a temp..
Wire Loom | Flex Tubing | Riser | Plenum | Nylon | Split Wiring Loom | Bentley Harris Convoshield

I am sure there are other company's but make sure it is high temp and possibly gas and oil resistant..
Don't use regular tape as it will get hot and the glue will be everywhere..