Poor Throttle Response linked to Exhaust Manifold? Need Some Feedback

[northguest47]

I've noticed over the last year that my throttle response has been getting poorer. What I mean exactly by this is the time delay in milliseconds, or tenths of a second say between flooring the gas pedal in neutral and the motor responding and winding up. Here are my observations:
-since for long long time I would guess this delay to be say 200 milliseconds or so
-today this delay is now more like half a second!
-also it takes longer for the motor to spool down so when upshifting I have to wait a bit longer
-it takes longer to 'spool' up so when downshifting I have to 'blip' the throttle sooner and slower to match the rpm's properly

Here's another observation - today in neutral if I very quickly stomp the gas pedal to the floor and immediately release it the time delay is so big that the motor doesn't even rev. Its as if it doesn't even register that the gas pedal moved. If I quickly push the pedal to the floor and delay by just 2/10ths of a second, then quickly release the motor will spool up, but just a bit. It doesn't register the whole floor stomp but at least it 'sees' that it was supposed to rev a bit. If I push the pedal to the floor and delay for say just about half a second, then the motor will spool up really high as if its finally catching up to the pedals input. Similarly if I slowly push the pedal to the floor the motor will pretty much 'keep up' and rev all the way to red-line. And after releasing from red-line back to idle, its just waay slower than it used to be. In my mind I thought to myself, "oh what if the throttle body is all gummed up with crap and it won't close because its dragging on friction and dirt", but this just isn't the case. I'm no expert but there just isn't any dirt in the throttle body, it looks just fine to me. In fact its quite a strong butterfly valve its tough to hold it open to clean it!

Now I went to a shop just for some quick advice and I kid you not the guy had me rev my car in neutral over and over again, sometimes almost up to red-line, like really revving the motor (which I actually never do in neutral btw). He had his eyes closed, just listening to the sound, and then he told me he thinks its something to do with the exhaust manifold. Now I must say my exhaust manifold is rusty as heck and for all I know it could have some cracks/leaks in it. Could that cause some weird behaviour in how the motor reacts to telling the tb to open up? I was hoping that header thread was going to go on and would have the whole thing replaced next year, cat and all.

I've cleaned my throttle body and have a bottle of throttle body cleaner that I hit it with from time to time, but honestly, its never looked dirty, theres no buildup in it as I've never run my car with a cracked intake hose.

Any thoughts? I'm going to replace the air filter and clean the throttle body next week along with some other winter mods. Hoping to get some input. Lates

[northguest47]

When my car was in the shop it was found that the flex pipe outer casing had been ripped off or torn off, and that this flex pipe was leaking.. it was replaced and the car now seems to rev fine, as in back to how it used to... still that delay, but back to normal. I can downshift much easier now. Dunno how I didn't notice this leak.. perhaps it happened over the summer slowly as the flex pipe got worse and worse.. I did high side several times on some dirt roads. Anyways I don't fully understand how an exhaust leak after the cat could cause this behaviour but being there would be some pressure loss just have to say glad it wasn't anything big. Still hoping to replace the entire exhaust and header at some point.

[Daox]

Glad to hear you got it figured out.

[northguest47]

Thanks, Daox, I was thinking if forum folks knew what likely would cause this, they would have piped up. I'm just happy to have her back on the road and hopefully not to be worked on until late spring when I should finally have my own garage to work in!