Can you diagnose this?

[Technical_Automan]

Any thoughts on what is causing this problem: When the engine is cold, there is full power throughout the RPM range, no matter the throttle position. When the engine reaches normal operating temperature, at low throttle / low RPM the engine runs smooth. At about 40% - 100% throttle between 0 - 4000 RPM the engine lacks power and bogs, though RPM's still rise at normal speed. And at 40% - 100% throttle above 4000 RPM the engine smooths out and has full power again. What does that sound like (for any tech's out there, or anyone who has had the problem)?

[The Right Formula]

Originally Posted by Technical_Automan

Any thoughts on what is causing this problem: When the engine is cold, there is full power throughout the RPM range, no matter the throttle position. When the engine reaches normal operating temperature, at low throttle / low RPM the engine runs smooth. At about 40% - 100% throttle between 0 - 4000 RPM the engine lacks power and bogs, though RPM's still rise at normal speed. And at 40% - 100% throttle above 4000 RPM the engine smooths out and has full power again. What does that sound like (for any tech's out there, or anyone who has had the problem)?

Throttle Position Sensor (TPS) perhaps? Sounds exactly like something that happened to my Grand Am about a year ago. Word of advice--if you have it diagnosed and the TPS is the culprit, by all means try to change it yourself. Shops charge a hefty penny for the replacement and it's relatively easy (to a degree).

--Jay

[Technical_Automan]

Hmm, well if it was TPS wouldn't you think it would have rough idle, and wouldn't it have loss of power all the time, not just when it warms up. BTW my exhaust had a small leak in it which I closed up yesterday, I noticed that the power loss decreased a little bit. It still bogs out, a lot, but less than before. One of my header's has a broken pipe on it, one of the pipes that come off the header, not a main pipe. And I can't remember but I think the problem started when I welded the converter on to replace bolts. I don't know if any of that might trigger something in anyone's head as to what the problem might be. And don't worry, on this car I do ALL the work myself...good learning car.

[TransAm_Ownr]

yeah im startin to have that same problem....When I press the gas about 3/4 the way the gauge will drop very little and then keep going like it should. I dont really know what problem this is so if they help you then it will probably help me.

But anyways I tried cleaning my fuel system because that was one idea to me. That worked for a little while but is still doing it so its not the problem.

Im hopein that its just an easy to fix problem. So I dont have to go all out on it just yet. But also my engine has 98000 miles on it.

[lefty13lefty]

the tps is know for going out in grand am's i reccomend you change it mine went out and i changed it and the whole thing smoothed out, its located on the side of the throttle plate (body) it takes two bolts to remove and is easy to replace it runs about $30, it worked on mine, try yours, Good Luck, the car will run rough when it cold anyways they are made to run warm and thats why they reccomend you let the car run for approx. 3 to 5 mins before driving it, Good Luck

[Technical_Automan]

Originally Posted by lefty13lefty

the car will run rough when it cold anyways they are made to run warm and thats why they reccomend you let the car run for approx. 3 to 5 mins before driving it, Good Luck

Oh you must have read wrong, that's what's weird about this problem, it only runs smooth when it is cold, and rough when it warms up. But thanks for the tip, i'll look into the TPS since a few people have mentioned it so far and it's a pretty cheap part.

[Technical_Automan]

*UPDATE* I replaced a few vaccuum hoses and the breather thing that goes into the valve cover, and the check engine light went off. But the car still bogs out when it's warmed up. I'm starting to think the problem is an open loop, closed loop thing. Not 100% sure, but when the engine is warm, and I start it and floor it within less than 30 seconds or so, it has full power throughout the RPM range. Now my question is, are there any sensors besides the oxygen sensor that don't send a signal until the car is warm or after a certain amount of time (open / closed loop)?

[TransAm_Ownr]

have you flushed transmission???

[Technical_Automan]

nope I was thinking about doing that and changing the rear diff. oil but I didn't think that was causing the problem, since it runs perfect when its cold...seems more like a sensor problem. But if you know something I don't please tell me.

[TransAm_Ownr]

well the filter could be clogged becasue this guy i know was talkin to me about what all could be wrong and he said that it could be unbalanced tires ( dont ask ), the transmission could need the filter and new fluid, suspension, or the engine mounts.

[Technical_Automan]

I can kind of see how the transmission fluid might be it, but I don't know about the rest. I know my U-joints on my driveshaft are almost no good. But that all seems like it would be a problem all the time, not just when the engine warms up.

[savagewolf]

ok here are some sudgestions: assuming its an automatic, have the tranny flushed anyway, then u can zero out that posibility. part of it may be the temp guage, on my 90' formula if it gets to a high temp, the computer reduces the ammount of gas going into the engine to reduce the ammount of heat being produced. then again it could be the mas air flow (MAF) sensor, or the O2 sensor. another sudgestion is to check the vaccuums on the valve covers and if it has a carb, check the vaccuum there as well. it may be loss of compression also (check the head gasket and other pressure seals.) it may also be a bad ignition system or a cam problem (check distributor cap, rotor, and cam.) it might just need a simple tune up. you also might want to check your fuel pressure. i had a similar problem with mine, it idled fine but when i let off the clutch just enough to nudge the car forward, it boged or died. it turned out to be the fuel pump, and because u mentioned patching the exahust leak, if you had it on drive up ramps or the car was sloped so u could get under it and u start it up at that angle a few times... well there goes your fuel pump. pray that its not because unless u have a lift that u can use to drop the back end and get the fuel pump out, ur looking at a hefty mechanic fee. it cost me 300 for the pump without instalation and can go up to thousands of dolars. check your fuel lines for clogs. check your speed sensor also, it prob isnt the prob but its worth checking. you can usually tell its bad when the car wont shift itself untill 30 or 40 mph. u may also want to check the oil in the car.

[Meeghann]

It sounds like it could be the temp sensor. Very cheap and easy fix. Try it.

[Kurtdg19]

I would also check your EGR valve and make sure its still working properly. When your engine is cold, reach under the valve and push up and down on the diaphragm. You should be able to press the diaphragm up and down by using moderate pressure. If it doesn't move or takes a lot of pressure to move, I would replace it. I would also replace your PCV valve and possibly replace the fuel filter if it needs it. This should give a little better response. PCV is around $2, fuel filter $5, EGR valve around $35.

The EGR feeds small amounts of gas back into the combustion chamber. The valvue is usally open when your engine is warm and anytime your engine is running above idle speed. The ECM uses information from the coolant temperature, throttle position sensor, and manifold pressure sensor. The EGR valve should turn off at full throttle, if its still open, it could be a factor in robbing some power.

It could also be a clogged catalytic convertor.

[Technical_Automan]

So basically what you're all saying is it can be anything and I should check every damn sensor and mechanism in the car. lol