05-15-2005, 01:24 PM
OK, I finally began troubleshooting my car's hesitation at wide open throttle. My first step was to test the throttle position sensor following the directions posted by Mike944 in April of '04 on 968.net. Placing an analog voltmeter between pins 1 and 3 of the TPS, while my wife slowly depressed the throttle, the voltage went from 0.4V to 4.4V when the throttle was at the floor. The increase in voltage was very smooth and steady, with no abrupt jumps. However, the max reading of 4.4V is 12% below the 5V that should have been achieved. I tested my voltmeter on a 1.5V and a 9V battery, and got readings of 1.6V and about 9.1V, respectively, so I'm confident the voltmeter is reasonably accurate.
So, when the throttle is on the floor, the DME "thinks" it's only at 88% of WOT, so it will deliver an accordingly lower quantity of fuel to the injectors. This combined with a reasonable probability that the injectors are somewhat clogged at 86.5K miles, would seem to explain my car's hesitation when I floor it.
Has anybody else had a TPS fail, and if so, did it display similar readings? I'm assuming the fact that it reads so far below the 5V target is indicative of a real problem, not just a tolerance issue. Does anybody know if a TPS can be adjusted/repaired, or do I just need to replace it? I couldn't find one at paragon.com; I wonder what they cost. Can't imagine it's too pricey.
I talked to the previous owner, and he told me the spark plugs were replaced with the plug wires about 4000 miles ago, so I strongly doubt these items are the cause, but I plan to take a look at the plugs anyway to see if I can see symptoms of any issues (fouling, etc.). The distributor cap and rotor look fine. So my tentative plan is to order a new TPS, see if it improves things, then most likely send the injectors in for cleaning/blueprinting. I'll keep everybody posted.
Andy N
So, when the throttle is on the floor, the DME "thinks" it's only at 88% of WOT, so it will deliver an accordingly lower quantity of fuel to the injectors. This combined with a reasonable probability that the injectors are somewhat clogged at 86.5K miles, would seem to explain my car's hesitation when I floor it.
Has anybody else had a TPS fail, and if so, did it display similar readings? I'm assuming the fact that it reads so far below the 5V target is indicative of a real problem, not just a tolerance issue. Does anybody know if a TPS can be adjusted/repaired, or do I just need to replace it? I couldn't find one at paragon.com; I wonder what they cost. Can't imagine it's too pricey.
I talked to the previous owner, and he told me the spark plugs were replaced with the plug wires about 4000 miles ago, so I strongly doubt these items are the cause, but I plan to take a look at the plugs anyway to see if I can see symptoms of any issues (fouling, etc.). The distributor cap and rotor look fine. So my tentative plan is to order a new TPS, see if it improves things, then most likely send the injectors in for cleaning/blueprinting. I'll keep everybody posted.
Andy N