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Newbie needs help


ricky94sts

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Hi i have a 94 cadillac sts with the northstar engine and i have the check engine light come on and i got codes. p030,p036,p074,p038 and p044 need help on fixing where do I start. car runs good just idles high. it just started this not that long ago but want to get it fixed so i can drive in luxury again :rolleyes: any help would be great and also wher i could get parts to fix these problems. Thanks in advance everyone. Ricky

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P030 (E030) ISC RPM out of range

P036 (E036) EGR Valve Pintle Position Out of Range

P038 (E038) Open MAT Sensor Signal

P044 (E044) Right Oxygen Sensor Signal Lean

P074 (E074) Intermittent MAT Signal

The MAT is the manifold air temperature. The ISC is the idle speed control. It looks like the connector to the ISC, MAT and possibly EGR valvue is loose or disconnected. This is a lot more likely than all three of these things giving trouble at the same time, and they are close together so I would bet that they are on the same wiring harness line.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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P030 (E030) ISC RPM out of range

P036 (E036) EGR Valve Pintle Position Out of Range

P038 (E038) Open MAT Sensor Signal

P044 (E044) Right Oxygen Sensor Signal Lean

P074 (E074) Intermittent MAT Signal

The MAT is the manifold air temperature. The ISC is the idle speed control. It looks like the connector to the ISC, MAT and possibly EGR valvue is loose or disconnected. This is a lot more likely than all three of these things giving trouble at the same time, and they are close together so I would bet that they are on the same wiring harness line.

hi could you tell me where they are located and i will go check them now. thanks Ricky

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ISC motor is mounted on the side of the TB and has a plunger that acts on the throttle linkage.

EGR valve is a black canister mounted to the firewall side of the TB near the brake booster.

Right O2 sensor would be on the right bank exhaust manifold (I'm guessing the '94 only had 2).

Not sure exactly where the MAT sensor is located.

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The MAT sensor is manifold air temperature, so it will be near the throttle body. Follow the wire from the ISC to a plug. Two or three other wires should join it before the plug -- the MAT, front oxygen sensor (high on the front exhaust manifold), and EGR (in front of the water pump on the driver's side).

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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The MAT sensor is manifold air temperature, so it will be near the throttle body. Follow the wire from the ISC to a plug. Two or three other wires should join it before the plug -- the MAT, front oxygen sensor (high on the front exhaust manifold), and EGR (in front of the water pump on the driver's side).

Hi got any pics because I cant seem to find anything? sorry im new at this. thanks

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ISC motor is mounted on the side of the TB and has a plunger that acts on the throttle linkage.

EGR valve is a black canister mounted to the firewall side of the TB near the brake booster.

Right O2 sensor would be on the right bank exhaust manifold (I'm guessing the '94 only had 2).

Not sure exactly where the MAT sensor is located.

Hi got any pics cant seam to find this stuff could be lookin right at it and just dont know it. thanks

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My car is a 1997, which has different intake manifold and EGR from the 1993-1994 Northstar. My car doesn't have a MAT sensor, and uses an intake air temperature (IAT) sensor in the air cleaner instead of a MAT because of differences in the fuel injection (your intake manifold is metal, mine is plastic). My EGR is external, yours is internal. The idle air control (IAC) should be the same. All this throws doubt on the schematics in my factory shop manual (FSM).

My FSM shows that the IAT (the equivalent of your MAT), the IAC, and the EGR to be on their own cable to the PCM with no connectors other than on the devices and at the PCM, except for a separate line to power for the EGR valve control. If your car is hooked up similarly, I would look at all three connectors and the connector to the PCM. Also, check all the 10 A fuses in the engine compartment fuse block, which is on the driver's side behind the air cleaner, with a black plastic cover over it. In particular, look at the fuses marked ECS, OXY SEN 1, and OXY SEN 2.

My EGR valve is mounted on the rear cam cover on the driver's side. The front (or, right) oxygen sensor is on the exhaust manifold below the engine oil dipstick, and the cable to it should be visible from above.

The figure showing the IAC connector on the throttle body from my 1997 FSM is shown below. Click on the image to get a full-size view for printing.

th_FSM_8A-201-14_Fig_28.jpg

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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The idle air control (IAC) should be the same.

Jim, the '94 used the ISC (idle speed control) motor to control idle. Not sure what year they switched to IAC (idle air control) valve. I think it was around '95 or '96.

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Ok guys I'm pretty sure I found the idle control motor there is a loud kinda grinding noise coming from it when you turn the key to the on position and when you turn the key off also. Could this part be bad?

Some noise from the ISC is normal. As long as you're not getting a racing idle it should be fine.

The ISC motor is located on the bottom of the throttle cable linkage assy. at the throttle body.

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That idle speed it way too high for a warm engine. The idle control motor is a stepping motor so a brief buzzing sound on startup is normal, but what you describe sounds like stripped gears. I would replace it.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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