Ok, I'm going nuts trying to figure this out. Hopefully someone can point me in the right direction.

Lately my car has had a surging idle. From 1500 down to just about stalling, to finally stalling. Every stop I have to play with the pedal to stay running. Along with that when I do get the car to move forward I get a horrible bogging and stumble with any type of accelleration. It seems if I keep the rpms about 3k-ish its ok. Any small increment of acceleration from idle up to that just stumbles like crazy. Past that I can go WOT with no problems.

I've checked for vacuum leaks, haven't found any. My spark plugs aren't even 3 months old, same with the wires, cap, rotor and coil. The wires are done correctly.

Now my mindset said well maybe its the igniton module. I've had one crap out on me before and I figured that would be the weakest link in the ignition. I replaced that and no change.

So now I'm thinking its probably fuel. It does feel like its bogging like it does when I'm low on fuel. I think maybe the fuel filter is clogged. I replace that. Same problem, no change. So now I'm dreading it may be the fuel pump.

Is there any other alternative I may have missed? Some background: The car sat for about a month and a half because a washer from my ram air box got sucked into the intake (EXTREMELY regretting descreening the MAF... live and learn...). So I had the heads off and everything. Reassembled and torqued down to spec and all that. I removed the AC back in July or so. Smog pump and air tubes are also removed.

^ As I typed that I realized the MAF may be bad now... not throwing any codes though...

Anyway, this is driving me crazy. I'm hoping maybe a second set of "eyes" can help me see anything I might of overlooked or missed. Thanks ahead of time.

Oh, and just so I don't get "reminded" about the search button, I did search, and that led me to the filter and module and vacuum leak.

 

Do you still have an EGR valve? They are known to cause lots of problems similar to a vac leak in the lower RPMs like you're seeing whe they quit working right (either the valve, solenoid, or hose)

 

Washer went through the MAF? It may have broken the wire element in it. To check it disconnect the MAF from the air ducting but leave the electrical connector on it, have someone start the car for a second and while you are looking into the MAF have them shut it off and watch for the wire element to glow as the burn off cycle happens. If that checks out then the element is in tact and I would next look at replacing the coolant temp sensor.

 

A check on the TPS may indicate if its OK. Could give you trouble there too.

 

Well I pulled the MAF off and low and behold the wire was snapped. I could of swore that it was in tact when I put the engine back together, but whatever.. whats done is done, I got a new one. 160 hurts, but I needed to be spent.

Now my idle seems steady at around 600-750 but the bogging and stumbling is 5 times worse. It drove like complete crap from AutoZone to my house with the new MAF in. I figured maybe I have to unplug the battery to clear any codes in the ECM? Would that help? I don't really know for sure, but I did it anyway.

Yes, the EGR is still on the manfold. I was going to remove it but I didn't have the funds for the block off plate and needed the car back on the road quickly. It is all rusty looking though, and one of the bolts was a completey PITA to get out, in fact we couldn't get it out, thats why we didn't remove it. How would I be able to check if its bad elsewise?

And about my thoughts on the fuel pump. I mentioned it to my friend and we both agreed that we heard the pump buzzing away. The buzzing didn't change speed at all or anything when the idle dropped down.

Still stumped here, hopefully its something easy that I've overlooked.

Oh, would a possible vacuum leak at the EGR valve cause this bad of a problem? Because that was one of the gaskets we couldn't change.

Thanks again.

 

Yes unplug battery reset codes...
The maf you got is it a Gm "heated wire" setup...or is it a film one like the wells unit..I tried the wells type unit...car did not run right in the high rpms..even after resetting code..went back to oem unit, car runs fine...
Yes a vaccum leak big enough can cuase tons of problems..
For example the vaccum line to my cruise control broke off(I never use it so I Didn't realize it was not working)and at the same time I had a rough idel that would surge/drop ect..almost stall at the light..turns out that small vaccum line that broke on the t-connector off the back of the plenum was enough to cause all the idel problems...
Also a coolant temp sensor can cause problems if it is not working properly...I think at WOT it is ignored (I think) thus the car will take off floored.. yet run bad part throttle..not positive on that,so someone correct me if I'm wrong.

 

The battery has been undone since my last post, haven't gotten the urge to go out and check, I'll try it in the morning.

The MAF was a remanned Bosch unit with the heated wire.

I removed the Cruise Control a while before any of these problems started occurring. I plugged all the little lines, but there was this one fairly thick one that I didn't have a plug for. When the car is running, it doesn't suck in or blow out, I'm not sure if that may be part of the problem.

The coolant temp is the sensor on the driver side of the block between the first and second spark plug with the sliding clip thing? If so, that looks fine, the wire is ok also, and I get temp readings just fine.

I'll be running out of options pretty soon so I should have this problem nailed.

Thanks for all the help everybody.

 

No, that is the coolant temp sender...for the gauge. The sensor is on the front of the intake manifold, the smaller of the 2 items in there.

 

I had the battery disconnected all night, and still no change.

It seems that when the car gets warmer and closer to operating temp, it does it less and its somewhat less severe. Its like I try to pull from a stop sign, I get maybe 5 feet and the car stops cold, like its not getting any fuel, then without moving the pedal at all, it will start moving again. This happens everywhere under 2500 rpms.
The choppy idle sometimes goes away and it idles ok at around 750, but then the bogging is horrible. If I romp on it and keep it at WOT for about 30 seconds or so the problem will go away. It will idle at stop signs around 1100ish and no stumbling. Then by the time I hit the next stop sign, the problem is back.

I think I know what plug your talking about now. Its the sensor right to the side of the coolant line, under the IAC sorta. Could this cause such a serious problem like mine? It doesn't seem to hard to replace.

Someone suggest to me it may be bad gas since the car was sitting for a while, but I'm already on the second tank since I got the car back. Then they suggest maybe dirt or something got in the injectors or something to that sort. I'm assuming clogged injectors could cause a major problem? I put in some STP Complete Fuel System cleaner stuff in my tank along with some of that ISO HEET anti line freeze and water remover stuff when I changed the fuel filter.

This has turned into a bigger problem to figure out than I originally thought.... but don't they all?

Thanks again for everyone's help. Keep the suggestions coming.

 

I can only suggest checking that the IAC is setup properly.
Sounds like its opening too far then closing down to get you going again. Maybe readjusting will get the idle to be a little better, if not at least you know that part is setup good.
https://www.thirdgen.org/newdesign/tech/tpimod2.shtml

 

The TPS and IAC were replaced when I put on the BBK throttle body about a year anda half ago. I can't really see how they would get out of whack by just removing the TB, since I'd had the TB off before with no problems, but I might as well check it anyway.

My friend said he talked to a mechanic at a Pontiac dealer and he said it sounds like an injector problem. One (or more) of them may be clogged or bad. The injectors were new with the 350, they had to be upgraded from the 305. That was November of 03.

How can I check to see if an injector is clogged or bad? I put in some fuel system cleaner like I said, but is injector cleaner any different?

 

For the injectors, you should get out a DMM and make sure they all have about the same resistance. Anything too far from the others is probably bad. If that is good, then you need to flow test them. They make testers for that.

 

If you haven't done it already, replace your fuel filter.
Also check your fuel pressure. I had an '86 z28 that acted exactly like yours, problem was caused by a weak, but not yet dead, fuel pump, the best it could do was about 30 psi.

 

Unhook vacuum line to the EGR valve and plug the line. Light will come on but it won't really affect anything else. See how it runs like this. Sometimes works wonders.

 

This past week I had been having the same problem with my 89 'Bird, very hard starting, and once it did start it idled rough, stumbled and sometimes stalled, drove me nutz. I replaced the maf sensor and relays, the fuel pump, and relay, the cts, o2 sensor, and the egr valve, none of it was any help. Problem turned out to be a bad oil pressure switch.
I replaced the o/p switch saturday, the car has run like new ever since (it should, considering all the new parts)

hope this helps

 

How does the oil pressure sender effect the way the car runs? Can't see a connection. Not getting smart, just would like to know.

 

FireBoid,

The oil pressure switch is a back up to the fuel pump relay, when the switch closes it sends 12 volts directly to the fuel pump. That way if your fuel pump relay ever fails, your fuel pump will still run.

In my case both the switch and relay were weak, also, the 12 v power for the maf sensor is only switched on when the fuel pump is running. So if fuel pump is acting up, the maf sensor may also have issues.

On the older third gens the oil pressure switch and the oil pressure sender were 2 different parts, on the newer ones they were both in the same part.

Hope this clears it up for ya

Oh yeah, I had to replace the o/p switch again, the one I got at Auto Zone was defective, the pump wouldn't shut off !

 

Yes it does. Thanks. So you were getting an intermitant signal to the fuel pump relay causing fuel feed troubles.

 

I Had the same problems. I had to not only replace the MAF, but also both relays - the power and the burnoff. Then after that, I replaced the O2 sensor. There seemed to be incremental improvements for some reason every step of the way. First it barely ran until I replaced the MAF (I too descreened - wont do that again), it ran better but still sumbled. The relays were next - better yet but stumbled at WOT. After the O2 sensor, the car ran great and has ever since.

I am no expert here but I wonder if one of the parts going bad after a while affects the other parts and helps burn them out faster. Any way, When I had to figure this out is drove me crazy - I hope you get yours fixed - I know how it feels.