FAQ: Vacuum Hoses & Lines (Series II SC)

I could be the MAF, PO102 is MAF sensor circuit low frequency listed things to check for in FSM are

Object blocking MAF inlet screen
Vacuum leaks around the intake manifold
Vacuum leaks around throttle body
Vacuum leaks around EGR valve Flange and pipes
Crankcase ventilation valve faulty, missing or incorrectly installed

after that has been checked manual says to check MAF circuit for shorts or open circuits.

If no problem is still found it says replace MAF, and if problem continues to replace PCM

Hopfully it is just a vacuum leak

I just remembered seeing a note about not using carb cleaner on the maf in the service manual due to the oil residue it leaves.

I checked the thread and saw you used Throttle body cleaner so I checked MSDS on internet to see if they have same ingredients, very close. There where also bunch of google hits about TB cleaner messing up idle and throwing maf codes.

Try using MAF cleaner on the sensor to take off the residue the TB cleaner left.

One thing you can try is temporarily disconnecting the MAF sensor and see if it runs better. It will run a little funny at first as it relearns fuel trims, and don't drive it too long with no MAF, it'll be a little unresponsive at times, but if the overall idling/easy throttle improves, that also point to MAF. Expect RPMs to dip unexpectedly from time to time, but it usually recovers.

Also, before you replace the MAF sensor, double check your wiring harness. We've had a lot of threads lately about discovering brittle/broken wires.

good info...

they replaced PCV valve I'll look at that, and I found A BUNCH of broken old rubber connectors for those lines. there may be another...

I'll also clean MAF with MAF cleaner (do they sell that??)

She'll be back up soon enough!

Thanks gang!

Natesriv wrote:

good info...

they replaced PCV valve I'll look at that, and I found A BUNCH of broken old rubber connectors for those lines. there may be another...

I'll also clean MAF with MAF cleaner (do they sell that??)

She'll be back up soon enough!

Thanks gang!

GM dealers have TB, MAF and other cleaning solvents - you may be able to get from them.

Otherwise I suggest you get CRC05110 - that's CRC's MAF cleaner - and follow label directions. Probably in a gray can, 11 oz should be less than $10; be sure to follow label directions. Most likely NAPA, maybe CarQuest or Pepboys.

Albertj

All the Auto Parts Stores sell MAF cleaner now.
Used to be a little hard to find, not anymore.

Okay, I had to replace a lot of rubber vacuum connectors. Since they're dealer only I "modded" some regular vacuum connectors and added new rubber & such. It seems to work. All the connections are in the right spot..nothing is loose.

Car runs fine at speed. But once warmed, it will idle high when you let off the gas for about 15 seconds... The SES/Traction light will go on (traction goes off, but SES is always on)

I cleaned MAF with MAF cleaner, unplugged battery (need more than 10 minutes? Unplugged positive terminal)

Went for a drive...same problem. I don't see any area that stands out. All connections are on, no loose lines, no broken rubber.

Do MAF's really go bad? Would it cause engine to stay high at idle?
What is MAP sensor do? (not MAF, but MAP)

I'm stumped!

Thoughts?

oh, and does anyone know where to get part numbers for all the vacuum line connnections? I'd like to go back to OEM...get ride of my jury rigged setup

Thanks!

Nate,
Sorry about the delay I was looking for the part numbers for what you are looking for and was not very successful!
This is the only diagram I can find for the vacuum harness and unfortunately it shows, as you can see, that 96-97 is N/A? Perhaps someone with a GM parts manual or microfiche can look further and be of more help?
I do have the microfiche but don’t have access to it right now, I’ll try and look sometime this weekend and see if it is more helpful.




Sorry I can’t be of more help!

Natesriv wrote:

Okay, I had to replace a lot of rubber vacuum connectors. Since they're dealer only I "modded" some regular vacuum connectors and added new rubber & such. It seems to work. All the connections are in the right spot..nothing is loose.

Car runs fine at speed. But once warmed, it will idle high when you let off the gas for about 15 seconds... The SES/Traction light will go on (traction goes off, but SES is always on)

I cleaned MAF with MAF cleaner, unplugged battery (need more than 10 minutes? Unplugged positive terminal)

Went for a drive...same problem. I don't see any area that stands out. All connections are on, no loose lines, no broken rubber.

Do MAF's really go bad? Would it cause engine to stay high at idle?
What is MAP sensor do? (not MAF, but MAP)

I'm stumped!

Thoughts?

MAP stands for Manifold Absolute Pressure; basically MAP is an electronic barometer for the intake manifold.

Albertj

that vac diagram is for a 97+ riv. our 96's are slightly different.
I do not think you can still get the vac lines from the dealer anymore. Most of my lines have been replaced with rubber vac hose from autozone. it comes in many sizes and works to repair any line except those special pieces that go from large to small.
Also, what code are you getting?
And to answer you questions, yes the MAF can go bad and it can cause a high idle condition (it would also cause the car to run rough at first startup too). the map sensor will set the SES light but not the TRAC OFF light.
My guess is either a cam/crank sensor or a MAF sensor. those are the only ones i've seen trigger the trac light.
You need to find the code and go from there.

99Rivman wrote:

Nate,
Sorry about the delay I was looking for the part numbers for what you are looking for and was not very successful!
This is the only diagram I can find for the vacuum harness and unfortunately it shows, as you can see, that 96-97 is N/A? Perhaps someone with a GM parts manual or microfiche can look further and be of more help?
I do have the microfiche but don’t have access to it right now, I’ll try and look sometime this weekend and see if it is more helpful.


Sorry I can’t be of more help!

No worries, thanks for the help. Actually, you can build your own system with off the shelf parts...it will will work, just not as "pretty'

I think I'll contact Ed Morad and get a new MAF and a new MAP and put them on, leave batter unplugged for a bit and see what happens...

From what I've looked at, I don't see any busted lines, or anything...just acting funky...SES and traction light on...

We'll see!

Thanks guys!

that applies to 97+ riv's. the 96's have a slightly different diagram due to the vac controlled transmission.
glad you found a nice diagram though, people area always asking where to check for lines.

I will try and find individual diagrams for the 95 and 96 also.

Don't forget: The damned factory diagram left out the EVAP Vacuum Switch...


I know my '97 has one, and since it's only there for OBDII testing of the EVAP system integrity, I would assume that all '96+ cars have it.
It's number 2 below, right next to the EVAP Purge Solenoid, behind/beneath the alternator.
(Yes, this diagram has the extra hose for the 4T60 tranny.)

Eldo wrote:

Don't forget: The damned factory diagram left out the EVAP Vacuum Switch...


I know my '97 has one, and since it's only there for OBDII testing of the EVAP system integrity, I would assume that all '96+ cars have it.
It's number 2 below, right next to the EVAP Purge Solenoid, behind/beneath the alternator.
(Yes, this diagram has the extra hose for the 4T60 tranny.)

Isn't the Evap Canister switch mounted under the car for the 1998 and later with the Evap Canister.?
If so, that is why the first diagram on here doesn't have it.
I believe the first diagram is only showing what's on the engine or under the hood for 1998 +.
But I will double check and report back and hopefully we can then have accurate files and diagrams for all years.!!

Rickw wrote:

Isn't the Evap Canister switch mounted under the car with the Evap Canister.
If so, that is why the first diagram on here doesn't have it.
I believe the first diagram is only showing what's on the engine or under the hood for 1998 +.

I repeat: "...right next to the EVAP Purge Solenoid, behind/beneath the alternator."
As far as I know, only the EVAP Vent solenoid is at the rear (and of course, the tank pressure sensor.)

Remember last month when one of our members had his vacuum switch come apart, setting codes, and we couldn't figure out what the hell he was talking about until he took a picture of it? You can see it without removing the engine cover if you shine a light under the alternator from the passenger side.

I'm just wondering if that is pre-1998 only.
Too dark here at the moment for me to check, but i don't remember a switch in that area. And I've had my Alternator off recently.
But that doesn't mean it isn't there as I wasn't specifically looking for it at the time.
I'll have to double check and report back.

Turns out you're right about pre-98. God knows why they changed it so fast after the initial roll-out of OBDII in '96, but while changing my fuel sender today I realized that I don't have a pressure switch at the tank... So, in '98 they put the switch in the top of the fuel module, and got rid of the one up front by the purge solenoid.

Eldo wrote:

Turns out you're right about pre-98. God knows why they changed it so fast after the initial roll-out of OBDII in '96, but while changing my fuel sender today I realized that I don't have a pressure switch at the tank... So, in '98 they put the switch in the top of the fuel module, and got rid of the one up front by the purge solenoid.

Yep, they all ('98-on) use an FTP sensor now on top of the sender.

I am replacing all the vacuum lines and fittings because they are beat and seem to be leaking? I cant find a leak but the vacuum gauge keeps fluctuating between 12 and 18. Does this type of vacuum system require a check valve? If so where would it benefit most in the vacuum path? Also will it effect boost? Being a check valve and maintaing one way pressure I think will keep gauge from reading boost if not placed in right place? Or is this not even needed? Comments? Suggestions? Help! Lol.

knuckled1 wrote:

I am replacing all the vacuum lines and fittings because they are beat and seem to be leaking? I cant find a leak but the vacuum gauge keeps fluctuating between 12 and 18. Does this type of vacuum system require a check valve? If so where would it benefit most in the vacuum path? Also will it effect boost? Being a check valve and maintaing one way pressure I think will keep gauge from reading boost if not placed in right place? Or is this not even needed? Comments? Suggestions? Help! Lol.

Suggestion: fix the leaky lines first including using a little RTV gasket goop on the fittings - then look at the gauge.

Added rtv to all fittings and still reads 18-20 on vacuum gauge. checked intake bolts and replaced all lines and fittings. Where could I be leakin from? Or is this normal vacuum for these cars?

by the way, it runs great, just gauge annoys me if its wrong! Check engine light came on this morning too. Off to find a scanner I guess?

My car is a 98 with a 97 motor. I had to rig the 97 s/c with 98 componets. I dont know if this is causing a problem or not, but they have different vacuum componets and slightly different vacuum as well. Should I revert to putting 97 componets back? Are there pictures available of the set up? Just a thought that turned suspect on me!

I'd get those DTCs read with a scan tool or code reader. If you're serious about maintaining your car, it would pay to invest in a scan tool to do your own diagnostic work. If you need to, most major auto parts stores offer the service free of charge. The codes are critical clues, and may tell you exactly what the problem is.