Throttle Sensor?

Question

I just bought a 1999 Chevy Blazer (V6-Automatic) with 55,000 miles on it. The car overall is excellent except for the acceleration. Once you gain speed over 15 to 20 mph, the acceleration comes to a crawl almost. It's like it's a 4-cylinder engine all of the sudden. Passing on the highway is a struggle, and mountain hills are out of the question. The Blazer is equipped with Chevy's "Vortec 4.3 Liter V6", their bigger engine for this model, but it sure don't feel like it. Could this be because of a defective throttle sensor, or is it an engine problem.

Answer 1

I own a shop, and a 4.3 Vortec Blazer that will burn rubber. The first thing I would do is replace the fuel filter, as this is probably the problem. Then I would replace the air filter because you need this anyway. With the fuel tank at about 3/4 full add a bottle of "STP Fuel Injector Cleaner" (black bottle only) to the tank. If you are not up to speed now, then start trying to find the culprit. Usually if you have a bad throttle position sensor, you will also experience some shifting problems with the transmission, but don't rule out the sensor just yet. These engines are really bad to have problems with the EGR valve, so start by looking at all the vacuum hoses you can on the engine to make sure they aren't split where they plug on, came off, collapsing, or just leaking due to holes in the lines. Making sure you are getting the vacuum to the components is essential to an engine running good. The 4.3 has a timing chain (very seldom goes bad) so I would think it it starving for fuel. You can bench test the throttle positon sensor with a meter or sensor tester, but I've had them test good but be bad. You may even have a weak fuel pump, leaking fuel pressure regulator, or a leaking intake that is causing this problem. You can use a vavuum gage to test the engine for many different problems. You could even have a plugged up cat converter. Take it to a reputable shop "if" my suggestions didn't resolve the issue, and have them give you an estimate of the repairs, and this way you will know for sure what the problem is.
Part 2:
Many people are quick to scan the computer for codes, but let me be quick to say; One does not always get a code, and must rely on the data stream information. Being educated in understanding, as well as knowing bad numbers from good numbers is everything in diagnosing computer related problems. In every class, seminar, or situation I have ever been involved with, the first thing one does is; eliminate a power, or ground problem as being the cause, and then start the diagnostics. The second most logical thing to do is; rule out a mechanical reason for the problem. There is what is called a trouble shooting tree, and if one follows it, they can't go wrong. If we followed it on your vehicle using your symptoms, it would go like this; Correct voltage & ground from battery to computer, fuel & air delivery to engine, transmission shifting to correct gear (torque converter staying in lock-up mode), and finally going down the tree to the components supplying information to the computer, such as O-2 sensor, EGR, Throttle position sensor, Temp sensor, Map sesnor, and on down to the computer being bad. When one looks at this problem logically; the engine is most likely starving for fuel, and/or air. You are very correct is thinking the Throttle Position Sensor, but you must rule out a plugged up fuel filter, a Fuel Pressure Regulator problem, and a plugged up Fuel Return line, before you spend money on parts that may or may not fix it.
Glad to help out, Good luck!!!

Answer 2

I doubt very much that it is a throttle position sensor. If the sensor becomes faulty, the PCM will pick that up and set a code, turn the SES light on the dash to tell you that, and will go into a failsafe mode to limp along until you get it fixed. What you have to do to decide what is wrong is get the PCM scanned for codes and proper data first. Then start checking into areas like air and fuel filter conditions, fuel pressure, tune condition and the like. Be attentive to secondary ignition parts as you might have cylinders not being delivered proper spark. These and all cars are too complicated to state something is wrong without a ton of diagnosis done beforehand. Good luck.

Answer 3

There could be many reasons why your car can't accelerate. It could be what you asked. It could also be your MAP / MAF sensor. It could also be fuel deliver (pump, pressure regulator, injector) or even the O2 sensor.

To me it sounds like you might have fuel pressure problem. You can use something like these to check:

http://www.sears.com/sr/javasr/search.do?BV_UseBVCookie=Yes&keyword=fuel+prssure&vertical=TOOL

As for the injector, you can get an auto stethoscope like these to listen to them for problems:

http://www.sears.com/sr/javasr/subcat.do?BV_UseBVCookie=Yes&vertical=TOOL&cat=Mechanics+Tools&subcat=Automotive+Testing+Equipment&keyword=stethoscope

Basically you touch each injector and listen. If any one or two injector sounds different (muffled or dead) then that / those need replacing. Some time just running a or two can(s) of injector cleaner in a full tank of gas is good enough.

There is also the remote possibility that your alternator is dying and not putting out enough power (Volt and current). So at higher RPM the sparks are not hot.

As I am typing I also remember that if your ignition is some how NOT being advanced, then you will lack power at higher RPM. For this you need to connect a timing light like these and see the change in ingition timing:

http://www.sears.com/sr/javasr/search.do?BV_UseBVCookie=Yes&keyword=timing+light&vertical=AUTO&cat=Tools+%26+Equipment

If you have a MAF sensor, try disconneting it and going on a test drive. The car ECU has limp home mode. If the car detects faile MAF sensor (and few other sensors), it will start iignoring it and calculate the air used based on other engine factors (like the RPM). If the car drives better then the MAF sensor is bad.

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You have to post more information for people here to figure out what is wrong.

Good Luck

P.S. Do you have clean air filter ??
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Answer 4

Yes the TPS can cause this problem when it is not reading at all we refer to this is "limp home mode" but since There is no possible way to diagnose a mechanical/electrical problem over the net so this is a few likley causes low fuel pressure(fuel pump week or fuel filter stopped) EGR valve sticking in the open position (very common) fuel pressure regulator malfunction, spider injector malfunction, MAS sensor not reading/unplugged,