Diagnose Saturn Intake Leak?: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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April 14, 2010 2:39 p.m. DWNSHFT Reader

Car is a 2001 Saturn SL1, 1.9 liter with automatic, about 92,000 miles. It's not throwing any CEL, but it has an intermittent high idle, between 1900 and 2400 RPM (in neutral). With the throttle closed, my scanner shows Throttle Position Sender wanders anywhere from 0.0% to 9.6%. I pulled the throttle body, cleaned it, cleaned (what I think is) the Idle Air Control Motor, and ensured no sticky throttle. Buttoned it back together and now it's worse, with idle as high as 3100 RPM, but sometimes returning to normal idle. But the intermittent high idle occurs more often now. I also wiggled the TPS and IAC motor connectors, and unplugged them, with no change.

Being frustrated and just as ignorant as before, I started playing with the air intake. With the throttle closed, I plugged the IAC air passage and the car still ran, with a high idle but not as high as before. In my ignorant ways it seems the car should stall when I do that. So I put my palm over the entire throttle intake, and while it makes a ton of vacuum and the idle drops way down, the engine still doesn't stall. So it seems that I have an air leak somewhere. Yes? No? Maybe?

While doing these very scientific tests I pulled the PCV hose and plugged it, so there was no intake air coming from that.

When re-installing the throttle body I used a new gasket (as the old one munched itself somehow). What other possible locations should I check for a leak? Manifold-to-block gasket of course, and there's something on the other end of the intake plenum, maybe the intake temp sensor, might leak there? What else should I check? Anyone have luck listening for an intake leak with a stethoscope (length of rubber tube)? I don't have any carb cleaner at home, any other GRM alternatives to carb cleaner as a spray-on leak detector? I'll buy some if that's what I need.

Any other advice? This whole modern EFI diagnostics thing is hard when I'm teaching myself from scratch.

Thanks a ton!

David
April 14, 2010 7:06 p.m. Twin_Cam Dork

That sounds like what I have on my '00 SL2 and no one can tell me what it is. However, I have a manual and have some other weird symptoms (shift light staying on after the next gear is selected, no neutral rev limiter etc).

I can rule out vacuum leak, because I've had that on a Saturn before, and it's just a consistently high idle at about 3 grand. Very annoying.

If you make any headway, let me know. I can't figure it out.
April 14, 2010 9:14 p.m. daytonaer Reader

My buddy had the L200. Had an intake leak. Fixed for a few months by replacing the entire manifold at the dealer. Took along time(and $$) to figure that out.

I have the L300, no intake leaks but its own unique problems. It is not the first time I have heard of the newer 4 cylinder (if that is indeed the same one) having hard to trace intake leaks.

You try using propane and a hose near intake trick yet?
April 14, 2010 10:45 p.m. DWNSHFT Reader

OK, I've never heard of using propane to find an intake leak. Please share!

David
April 15, 2010 12:01 a.m. curtis73 HalfDork

Brake cleaner or starting fluid is so much easier. Just spray it at the suspect areas and note if the idle changes. Hit everything... gasket gaps, vacuum hoses, throttle shaft, anywhere that has a potential for vacuum behind it.

But... you said the TPS wanders from 0-9.6???

You could have stopped right there. If your foot isn't pushing the pedal, the TPS should be reporting steady numbers. Replace it.
April 15, 2010 1:33 a.m. wrenchedexcess New Reader

I would focus on the TPS. As stated it should read about 600mv at idle. since it is a sweep resistor it has to mechanically move to increase voltage. If you are getting readings from 0 to 9.6v you may want to check the wiring going to the TPS. a DVOM will do the trick.
April 16, 2010 9:35 p.m. DWNSHFT Reader

I sprayed a bunch of carb cleaner around but there really aren't that many visible areas for possible leaks and none of them tested positive. Also, I got two more error codes, one for weak TPS signal and one for the IAC. So this afternoon I replaced the TPS ($35.99 from Autozone). Also used the opportunity to further clean the throttle body with the carb cleaner.

On the test drive I got one false TPS reading, 0.4% at closed throttle. Re-started the car and the rest of the test drive went fine. I'm concluding it fixed until I see other drivability issues.

Thanks to all for your input.

David
April 17, 2010 9:48 a.m. iceracer Dork

Use of a propane torch, UNLIT, to find vacuum leaks is a less messy method. Some chemical sprays are not all that flammable.
March 7, 2011 7:41 p.m. marthacondorelle

Hi everyone. Sorry to end up revising this thread. I came here for a reason though. I'm doing my Saturn repair and found out a problem - an intake leak and it looks to be pretty significant (having to add coolant once or twice a day depending on how much I drive). The radiator and hoses are fine and recently replaced.Here's my question: How can I 100% verify that it is the intake manifold gasket as I my local shop will do the gasket replacement for $280 (but charge more if a pressure test needs to be done) i want an assurance as well as save an immense amount of moolah. Please help. thanks!
March 7, 2011 8:05 p.m. Quasimo1 New Reader

In reply to marthacondorelle:

Go buy yourself a can of carb cleaner and spray it around each individual intake tubes while the car is running. If you hear the RPM's change you have found your leak. SL1 Saturns are known for this problem after 60K miles. If you car is like mine you can actually see the wrinkle in the intake gasket with everything in place on the car.

For more reference: http://www.saturnfans.com/forums/showthread.php?t=115925&highlight=intake+mani...
March 7, 2011 8:19 p.m. marthacondorelle New Reader

Thanks quazimo. really appreciated your help!
March 7, 2011 9:02 p.m. EvanB Dork

Coolant temp sensor? Maybe not the problem but they go bad quite often.
March 7, 2011 9:17 p.m. fasted58 New Reader

A digital tach will pick up the slightest fluctuation in rpm (10 rpm increments) while doing the carb cleaner or propane test, better than playing it by ear.
March 7, 2011 9:55 p.m. John Brown SuperDork

Quasimo1 wrote:

In reply to marthacondorelle:

Go buy yourself a can of carb cleaner and spray it around each individual intake tubes while the car is running. If you hear the RPM's change you have found your leak. SL1 Saturns are known for this problem after 60K miles. If you car is like mine you can actually see the wrinkle in the intake gasket with everything in place on the car.

For more reference: http://www.saturnfans.com/forums/showthread.php?t=115925&highlight=intake+mani...

I agree, and like your name (says the artist formerly known as QuasiMofo)
March 8, 2011 7:02 a.m. dmyntti New Reader

1.9L saturns have a tendancy to suck the intake gasket in at cylinder #1 though that would not cause a coolant leak. And if your car is a sinlge cam then they also tend to develop a crak in the head which could cause your coolant loss. I have a Saturn at my house right now that I got with both problems. On mine I had oil sludge in the coolant overflow from the cracked head and coolant loss.