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98 Pontiac Grand Am GT 2.4L DOHC: P0113 & P0118 Codes, Poor Idle, Smoke and Running Rich - What's Causing This?

Model: Girlfriends car Fault Code: P0113 Posted: 2006-09-22 21:20

I'm not a mechanic, so I'm reaching out for help with my girlfriend's 1998 Pontiac Grand Am GT (2.4L 4-cylinder DOHC). The check engine light came on, and using a code reader, we found two fault codes: P0113 (Intake Air Temperature Sensor 1 Circuit High Input) and P0118 (Engine Coolant Temperature Sensor Circuit High Input). I initially thought replacing just the intake air temperature (IAT) sensor and coolant temperature (ECT) sensor would fix it — but now I'm seeing more symptoms. After clearing the codes, the car takes a long time to crank over, and when it finally starts, it runs very rich, producing noticeable smoke. The idle is unstable, and the engine temperature reading spikes unexpectedly before dropping again. The check engine light returns after a few minutes, but the car seems to run normally afterward — at least temporarily. I'm concerned this isn't just a sensor issue. My friend, who's finishing up a technical program, suggested checking the wiring circuits to these sensors and measuring resistance, but I don't understand what that means. I'm now wondering: is it safe to replace only the sensors? Could a faulty connection or damaged wiring be causing both the codes and the poor performance? What should I check first — sensor values, wiring harnesses, or something else? Any advice on diagnosing this issue step-by-step would be greatly appreciated.

Related fault codes
P0113P0118
Comments (10)
Anonymous 2006-09-23 08:14

Are you looking for a clear explanation of what P0113 and P0118 mean in a 98 Pontiac Grand Am GT, or do you need help diagnosing the root cause behind the symptoms like smoke and rough idle?

Anonymous 2006-09-23 15:43

Jeff Compton wrote: Are you looking for a clear explanation of what P0113 and P0118 mean in a 98 Pontiac Grand Am GT, or do you need help diagnosing the root cause behind the symptoms like smoke and rough idle? Yes — I'd love to understand both the codes and how they relate to the car's actual behavior.

Anonymous 2006-09-23 19:59

Check the wiring harnesses and electrical connections for the IAT and ECT sensors. Look for corrosion, loose terminals, or damaged insulation — especially near the distributor and engine block areas.

Anonymous 2006-09-25 00:13

Jeff Compton wrote: Check the wiring harnesses and electrical connections for the IAT and ECT sensors. Look for corrosion, loose terminals, or damaged insulation — especially near the distributor and engine block areas. Thanks! That makes sense. I'm going to try inspecting those connections before calling a mechanic.

Anonymous 2006-09-25 09:10

If you're not comfortable with electrical diagnostics, it's wise to consult a professional — especially since symptoms like smoke and rich running suggest deeper issues beyond sensor failure.

Anonymous 2006-10-09 20:09

Jeff Compton wrote: Check the wiring harnesses and electrical connections for the IAT and ECT sensors. Look for corrosion, loose terminals, or damaged insulation — especially near the distributor and engine block areas. Jeff, where exactly are these sensors located? Can you point to specific locations on a 1998 Pontiac Grand Am GT? And what tools do I need to test resistance? Thanks in advance, Jay K.

Anonymous 2006-10-10 06:52

https://www.alldata.com - A reliable resource for wiring diagrams and sensor location references for the 1998 Pontiac Grand Am GT.

Anonymous 2006-10-10 17:32

Jeff Compton wrote: https://www.alldata.com - A reliable resource for wiring diagrams and sensor location references for the 1998 Pontiac Grand Am GT. Thanks for the link! The site is overwhelming, but I found a helpful section on sensor circuits. I'm now looking at specific wiring harnesses near the intake manifold and engine block. I'll go back to review it in detail. Jay K.

Anonymous 2006-10-11 08:12

I see — you're referring to a cold air intake elbow installation that may have caused a wiring issue? How did that affect the sensor readings or codes?

Anonymous 2006-10-18 12:02

To answer your question... Yes. The P0113 and P0118 codes were likely triggered by a faulty connection during my cold air intake elbow installation. I accidentally broke one of the wiring connectors on the distributor cap, which caused intermittent sensor signal issues. After replacing that connector, cleaning the contact area, and resetting the ECU, the codes cleared and the car runs much better now. Thanks for the help — this was a valuable lesson in proper installation procedures. Jay K.