Dealer can't fix it. Help!!!

[tonys93sts]

Ongoing problem with 99 STS(122K), but getting worse. When at a stop, or very slow speed(such as turning into a parking spot) N* will stall out or "surge" in rpms before shutting off. It always starts back up. Have replaced plugs, wires, crank position sensors, ignition module, mass air flow sensor,checked fuel pressure. Dealer has had on diagnostics 3 times,just "reprogrammed "the PCM, to no avail.Only code it is throwing is PCM 1599 stall or near stall.Dealer said no charge on last 2 diagnostics since they can't find it, but don't no where to go from here. It's getting dangerous to drive. Thanks for any and all help. Tony

[Regis]

Sounds to me like a leaky fuel pressure regulator (FPR). Probably dumping too much fuel in at low speeds and flooding causing the stall. Either that or a electrical issue such as a bad ground, alternator, and or battery. I'm sure more knowledgeable members will chime in with their assessments.

What kind of gas mileage are you getting? That may tell us a lot.

[Marika]

This may sound silly to you and everyone else but did you check your battery and replace the battery leads?

[BodybyFisher]

I am with Regis, check the fuel pressure regulator and clean the ISC (Idle Speed Control) if the 99 has one

[GreenMachine]

The 98 did this several times last winter, cleaning the throttle body solved my issue, it would get stuck on the build up I guess at low RPM's starve it for air.

[Marika]

My '92 seville did the same thing when I first bought it. Turned out to be a dying battery and bad battery leads.

[Ranger]

I am inclined to go with BBF. Clean the TB, especially if it has never been done. If that does not help, pull the IAC valve and clean out the passages. One would think that after all of this, the dealer would have tried that.

[Bill K]

When mine did the same stalling it turned out to need the EGR valve replaced.

[cyrez00]

to begin with i would replace my dealer.... a Cadillac dealer who gives up on a problem is not worth calling themselves a Cadillac dealer.

In my Factory Service Manual there is a trouble diagnostic tree to follow (out the top of my head its code p095 for my car i believe).

My FSM is from the 93 series though and probably wouldn't help you much. maybe there is anyone else who has the 99 FSM?

If you want a copy of the page anyway then just give a shout.

Marc.

[tonys93sts]

Thanks for ALL the great replies. The battery and cables were checked,swapped out egr from another "99(no change),no Idle speed control on '99, and was told ithad good fuel pressure(sending unit and pump have been replaced). The throttle body had been cleaned before( but looks kinda sooty now.) Any good links to thouroughly cleaning one? Thanks for all your help, Tony

[BodybyFisher]

I am inclined to go with BBF. Clean the TB, especially if it has never been done. If that does not help, pull the IAC valve and clean out the passages. One would think that after all of this, the dealer would have tried that.

very true. i would hope anyway

[Ranger]

The TB will start to get sooty soon after a cleaning. I do mine every spring. Just hold open the throttle plate, then spray, scrub & wipe till it is shiny. Doing it once a year makes it easy. The longer you let it go between cleanings, the harder it is to clean.

[NorthstarAJ]

Ongoing problem with 99 STS(122K), but getting worse. When at a stop, or very slow speed(such as turning into a parking spot) N* will stall out or "surge" in rpms before shutting off. It always starts back up. Have replaced plugs, wires, crank position sensors, ignition module, mass air flow sensor,checked fuel pressure. Dealer has had on diagnostics 3 times,just "reprogrammed "the PCM, to no avail.Only code it is throwing is PCM 1599 stall or near stall.Dealer said no charge on last 2 diagnostics since they can't find it, but don't no where to go from here. It's getting dangerous to drive. Thanks for any and all help. Tony

Location?

[tonys93sts]

Outside Nashville,TN.

[Regis]

Thanks for the message (PM) Tony. Let me post it in here and for future reference you'll want to direct further questions here so others can help and learn from your experience. Members such as BodybyFisher, Ranger, and others have excellent first hand knowledge as far as the FPR.

"Thanks for your reply! The fuel pump and sender have been replaced, and I was told that fuel pressure was "okay". I get 18-19 in town, 26-28 on highway. Is FPR cost much to replace? I know it's easy to get to. Thanks, Tony"

From the mileage that you're getting it doesn't seem, to me, that it's the FPR.... but who knows. Your gas mileage is right where it should be. I'm starting to lean towards an electrical issue (battery, alternator, bad ground, even a bad plug and or wires). Were all 8 plugs replaced and can you verify that they were? Not every mechanic likes to pull out the rear 4 plugs because they can be a little difficult but the dealer always seems to charge for 8 anyways.

[Logan]

The 1999 does use a GM IAC valve. IAC= idle air control.

GM has been using them 25 years. Cadillac only started using them with OBDII. (1996)

Anyway, common issue on these are they get sticky from carbon deposits. A issue a GM dealer would most likely know, but maybe not a Cadillac dealer.

I even have a special tool that can drive these in/out.

#1 in the picture. They can get dirty at the cone end, but I bet you'll see deposits on the shaft under the spring area.

I've had to clean mine on my 2001.

[Logan]

Having some PM messages from this owner because we are in TN. Maybe 40 miles apart..

Being now told a new IAC has been installed. Waiting to hear verification on that.

The IAC information still flies. Cleaning must be done. I suspect right now the root cause is a dirty TB and IAC.

Anyway, found this interesting bulletin tonight. Kinda hard to find some of these.

Document 1468338

Subject: 4.0L L47 4.6L LD8 L37 Engine Intermittent Slow Speed Decel - kw decelerate DTC EGR IAC MIL PCM P1599 stall #PI01803 - (03/04/2004)

Models: .

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When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.

Condition/Concern:

Some1996-1999 Oldsmobile Aurora with the 4.0L(L47) and Cadillac vehicles with the 4.6L (LD8 L37) Northstar engine may exhibit an intermittent stall/near stall/idle flare or flux while the vehicle is at idle. The customer may not notice the near stall but, will notice the idle flare as the PCM tries to save the engine from stalling. Normally this condition will be accompanied with a PCM code P1599 for stall or near stall detected.

Recommendation/Instructions:

This condition of an intermittent slow speed decel stall may be caused by carbon deposits formed on the IAC and EGR valve or in the throttle body passages. If this vehicle stalls when coasting above speeds of 20 mph, one possible cause maybe the EGR valve sticking. (As with speeds above 20 mph the P0401 diagnostic will exercise the EGR valve to near 100% when certain conditions have been met.). The sticking condition may not be on the pintle end of the valve, but on the shaft; therefore cleaning the EGR valve may not improve this stall condition. It is important to note that the P0401 diagnostic does not seem to run when the Tech 2 is in the snapshot mode. This prevents a technician from seeing the condition as it occurs. If the answer to either of these questions is yes, then the condition is not the EGR sticking from the P0401 diagnostic.

Does the vehicle stall when coasting with the speed below 20 mph?

Can the condition be captured on the Tech 2 or VDR in the snapshot mode?

If the answer to either of the above questions is no, then the decel stall condition maybe caused due to EMI induced on the crank sensor ckt .This EMI originates from the #4 cylinder firing event, through the spark plug wire into the ICM (from the #4 coil/ICM proximity), which is then transferred into the sensor ckt due to the proximity of the icm to the sensor ckt.

Verify spark plug and wire resistances are not excessive. S/P resistance should be 5000 ohms +/- 2500 ohms at approx 68 degrees F. S/P wires should not exceed 3000 ohms per foot.

Verify PCM grounds by using a voltmeter to check the voltage drop (should not exceed 40 MV ).

Verify fuel pressure during condition.

Check for possible carbon deposits formed on the IAC and EGR or in the throttle body passages.

Verify the ICM ground.

Verify all 4 ICM connectors are secure.

Verify crank A, B and cam sensor connector pins are not bent and that they are seated correctly circuit integrity.

Verify crank A, B and cam sensors are free of metal shavings. The metal shavings could distort the signal from the sensors to the ICM and cause misinterpretation of the data.

If the above checks are good and the condition can be easily duplicated, then swap #1 AND #4 spark plug wires at the coil and evaluate. if the condition is eliminated and spark plug and wire resistance checks are good, then install a revised crankshaft position a sensor(top sensor) . If condition remains, then swap #6 AND #7 spark plug wires. If this eliminates the condition, and spark plug and wire resistance checks are good, then install the revised crankshaft position sensor in position B (bottom sensor). Also, if the condition can be duplicated easily, the problem can be verified by using the Tech 2 manual snapshot feature to monitor engine RPM and 4X reference( engine 2 data). If engine RPM drops to approx. 400 RPM and 4X ref drops below 8 (usually 5 or 6) or above 8 (usually 10), this will most likely be seen in frame -1 just before stall in frame 0 of your manual snap shot.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

[steve6]

If all else fails, and you can't figure it out (I really doubt its this), but... check the back pressure. Make sure the catalytic converter isn't plugging up. Normally you would lose top end power as well with this issue, but starts as a idling/low speed issue usually. I have seen these go bad on cars and a lot of parts usually gets changed before its looked at....

I wish you luck, I have battled issues like this with other cars, and its very frustrating.