Throttle Response Bucks/Bogs at 2000-2500 rpm & Power Loss

**rgumm9** · 10-03-2006, 08:01 AM

Hello everyone...i am going out of my mind trying to figure out what the hell is wrong with my car. I have a 99 Firebird TA LS1 6speed.

The throttle seems to go out around 2000-2500 rpms and bucks/bogs the car. but once i get over the hump it seems to be fine. i notice it mostly in 1 and second gear but i have felt it while traveling at high speeds with lower rpm( in 5th and 6th gear). sometimes it is so bad that when it starts happening i can put the gas petal to the floor and nothing will happen. once i lift the petal up and then give it more throttle it will respond. This seems to happen more when i go up an incline or get on the gas. if i slowly put the petal down it seems to run fine. Plus, since these symptoms i have been feeling like the car has lost some power, not pulling like it used to.

First, here are the mods that have been done by a previous owner almost 2 years ago. It has the basics: intake, Headers, and 2 3/4" magnaflow exhaust.

the check engine light was on for quite awhile for my cats. i think the code was PO420 if i remember correctly. the car ran fine for a long time with the code. so i had the bank 1 cat replaced along with the O2 sensor bank 2 before the cat and the problem still exists.

i changed my fuel filter, when i fist took it off, there was alot of shit in it. alot. that was the first its been changed and the car has 69,000 on it. my fuel pressure is at 55 pounds. i am wondering if the filter needs to be changed again?

thinking maybe it was my spark plugs, i pulled one out and they look pretty good. but the gap looked big to me i think 60-70.

and the last thing i tried thinking the TPS was falling without throwing a code. so i pulled the plug on the TPS (throttle positioning sensor) on the intake to see if the car would run differently. and it did...so it seems the TPS is working fine.

Please, anyone if you have any idea of what is could be please help my out. it is driving me crazy, and it does not help that i am trying to sell it. i could not consciously sell a car that is not in tip top shape.

**SSpdDmon** · 10-03-2006, 09:19 AM

If it's not a clogged fuel filter, it sounds like the pump might be on the way out. Check/change the plugs, the fuel filter, and make sure there's not any gunk build up on the MAF (can be carefully cleaned with electronics cleaner). If that doesn't cure it, it's most likely the pump. If you park on an incline, is it hard to start after it cools off (ie over night)?

**rgumm9** · 10-03-2006, 06:01 PM

the car starts up and idols fine no matter how it is parked. Not to sound stupid, but what is a MAF? and where is it located?

now the problem is happening all the time. but out of gear it revs fine. only in gear around 2000-2500 rpms. i dont think its the fuel pump failing cause wouldnt it happen at all different rpms?

could it be a timing issue or something? i am so stressed out from this shit...i dumped so much money in this and the problem is still happening.

**Wesman** · 10-03-2006, 06:27 PM

Originally Posted by rgumm9

the car starts up and idols fine no matter how it is parked. Not to sound stupid, but what is a MAF? and where is it located?

now the problem is happening all the time. but out of gear it revs fine. only in gear around 2000-2500 rpms. i dont think its the fuel pump failing cause wouldnt it happen at all different rpms?

could it be a timing issue or something? i am so stressed out from this shit...i dumped so much money in this and the problem is still happening.

You need to start with the basics. Sounds to me like a simple tune up issue, having a spark plug gap of .060-.070 is way, way too much. Thats how my stock plugs were after 80K miles, and it produced the same symptoms you are describing. The car fell on its face and stumbled under throttle at 1000-2000RPM's. Change the plugs and wires, I'd reccommend AC Delco Iridium plugs and Granatelli wires ($99 from Summit Racing). That should make a huge difference in itself.

You say you already changed the fuel fiter, so that should be fine. Next up is to clean the MAF (Mass Air Flow Sensor). Its the screened sensor that sits between the air box and the throttle body. Its made of black plastic and has a metal filament inside of the housing. Take off the lid and rubber intake tube, and you'll see it right away. Pull it completely off the car and spray it down with CRC Mass Air Flow Sensor Cleaner (local Auto parts store should have some, try Advance Auto). Also buy some Chevron Techron Fuel Injection cleaner and dump either one large bottle (rarted for 20 gallons) or 2 small bottles (rated for 12 gallons each) into the fuel tank with about 1/4 of a tank of fuel left.

Before you change the plugs and wires, I'd also reccomment using Seafoam in the engine. Buy a can of it (local auto parts store, not the spray version) and feed it into the engine slowly using a funnel going into the brake booster line. Just setatch the line from the brake booster with a pair of plyers, hold it vertically, and feed the seafoam in slowly with the engine running. Use 1/2 to 3/4 of the can, and dump the rest into the gas tank or oil (change the oil afterwards). It will bog the engine down, and dirty smoke will come out the exhaust. Cleans it out nicely.

Try all those things first, since they are basic maintainence items, and see if it fixes the issue. if it does, you're good to go, if not, you know that the issue isn't anything that you cleaned/replaced.

Good luck, hope that helps.

**rgumm9** · 10-03-2006, 06:48 PM

thanks man...i will give it a try and let ya know how it goes

**99blueZ** · 10-03-2006, 07:53 PM

i agree with the above advice. I had the EXACT problem with my car for about 6 months. I kept trying everything: fuel filter, plugs&wires, pcv, cleaning the MAF, and a bunch of other stuff. And it was the MAF. Except mine was so gunged up that it needed to be replaced. Thats why finding out my car's issue was such a bitch. Cleaning my MAF did nothing it was basically dead.

But when i got that new MAF in there - WOW!! what a difference. Felt like a new car!

**GMS Fleet** · 10-04-2006, 12:19 PM

Summit doesn't have our wires at the moment. Try JEGS if you're interested in them.

**Ponti-MANIac** · 10-06-2006, 12:27 PM

Originally Posted by rgumm9

Hello everyone...i am going out of my mind trying to figure out what the hell is wrong with my car. I have a 99 Firebird TA LS1 6speed.

The throttle seems to go out around 2000-2500 rpms and bucks/bogs the car. but once i get over the hump it seems to be fine. i notice it mostly in 1 and second gear but i have felt it while traveling at high speeds with lower rpm( in 5th and 6th gear). sometimes it is so bad that when it starts happening i can put the gas petal to the floor and nothing will happen. once i lift the petal up and then give it more throttle it will respond. This seems to happen more when i go up an incline or get on the gas. if i slowly put the petal down it seems to run fine. Plus, since these symptoms i have been feeling like the car has lost some power, not pulling like it used to.

First, here are the mods that have been done by a previous owner almost 2 years ago. It has the basics: intake, Headers, and 2 3/4" magnaflow exhaust.

the check engine light was on for quite awhile for my cats. i think the code was PO420 if i remember correctly. the car ran fine for a long time with the code. so i had the bank 1 cat replaced along with the O2 sensor bank 2 before the cat and the problem still exists.

i changed my fuel filter, when i fist took it off, there was alot of shit in it. alot. that was the first its been changed and the car has 69,000 on it. my fuel pressure is at 55 pounds. i am wondering if the filter needs to be changed again?

thinking maybe it was my spark plugs, i pulled one out and they look pretty good. but the gap looked big to me i think 60-70.

and the last thing i tried thinking the TPS was falling without throwing a code. so i pulled the plug on the TPS (throttle positioning sensor) on the intake to see if the car would run differently. and it did...so it seems the TPS is working fine.

Please, anyone if you have any idea of what is could be please help my out. it is driving me crazy, and it does not help that i am trying to sell it. i could not consciously sell a car that is not in tip top shape.

Get yourself a 3 dollar bottle of drygas. Solved my problem in 10 minutes. The problem increases on an incline and whan you get on the gas because the the feed line from the tank is at the back and thats where the water goes when the ass end squats on acceleration or on an incline. It's also more of a problem at low RPM because the gas quantity spitting out of your injectors doesn't contain enough gas to compensate for the water. When you are at higher RPM's the engine is getting enough gas to make up for the water in the line.

**DemonSpeed** · 10-08-2006, 08:19 PM

I had a problem similar to that, went through everything new MAF, plugs, fuel pump, fuel filter.... turned out some wires were exposed underneath and they were getting wet from rain, washing etc..

**rgumm9** · 10-08-2006, 08:47 PM

thank you very much...it worked...i pulled out the MAF and some other sensors and cleaned them off...the car is running stong again...like new....thanks alot for all you help