Hey all, I've been trying to solve a stumbling problem with my car, I have an 88 305tbi. I've already changed the MAP sensor, TPS, rebuilt the tbi, and checked the wires, cap, rotor, coil, and plugs. When the car is running, it jumps from 600 to 1200. I can unplug the MAP sensor and the car will idle at 1100. I was wondering what else might be causing it to stumble, thanks in advance

 

Sorry can't help, but not sure if I've told you about Thirdgen Nat'ls '03. More info is in the link in my sig for my site.

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Simply put, I need more info. Your subject states that it stumbles but under what conditions is it "stumbling"? That would be a good starting point...


Brian P
89 IROC-Z 355

 

anytime the engine is running, unless the MAP sensor vacuum tube is unplugged. when it's unplugged it'll idle at 1100, when it's plugged it'll try to idle at 600 then go to 1200 and back to 600 etc. I just changed the MAP sensor, so unless I got a bad one, I don't think that would be the problem. when I put the car in drive, I can feel the car trying to take off on me, the rpm's will go high, my car will jerk, then the rpm's drop, the car will sit normal

 

I'd check for vacuum leaks as this allows unmetered air past the MAP sensor. If you have a scanner I'd look at the 02mV's and BLM/INT and see what it is doing. If it's adding fuel or running lean then you have a vacuum leak somewhere. Does it stumble at a steady cruise of 2000-2500 RPMs??

Brian P
89 IROC-Z 355

 

I just replaced most the vacuum lines after it started doing that. I don't have a scanner. the car will run almost great with the MAP vacuum unplugged, but with it plugged, when I rev the engine, it'll go up, then act like it needs air and just about die while foot is on the gas, the exhaust sounds nasty when this happens. when I take my foot off the gas it'll go back to the idle search.

 

I know that MAP sensors need good ground, have you checked this when you replaced it? Sorry I'm a MAF guy, and I know that our MAFs have a relay. Does the MAP have a relay? You may check that. You really need a scantool. If you do a search on the DIY-PROM forum for Craig Moates software you'll get a free scanner to run on a laptop, all you need is a cable that you can get from http://akmcables.com for $85. Well worth it, as I would have sold my IROC-Z without it (Long story).

Brian P

 

as soon as I get some more money, I'll look into that, that's a very good idea, thanks

 

well today I put in a new fuel pump and lo and behold it's ALIVE WOOHOO