Buick Century troubleshooting help

[MuzzleFlash40]

I just had the LIM replaced in the 2000 Buick Century 3.1

There is no trouble codes. At low speeds it will accelerate normally. If you floor it though it will feel like it’s lacking power. At highway speeds even if you floor it will do nothing. The engine will not respond at all. Going up a hill with your foot to the floor the engine will not respond. It won’t rev up at all. It idles perfectly, there doesn’t seem to be a miss.

At first I was thinking a vacuum leak but there is no misfires or bucking.

The idle air control valve is brand new due to it idling high randomly so I tried that first.

Could it be a Mass airflow sensor? I know those can cause issues without a trouble code. I had an old grand Marquis act similar and it was a bad MAF.

Kind of at a loss

 

[ls1mike]

Any codes? Mileage? Did you replace the gasket yourself?

 

[MuzzleFlash40]

Any codes? Mileage? Did you replace the gasket yourself?

As I said theres no trouble codes, and I had it done. It’s got 88k

 

[Lubener]

When you stomp on the gas, vacuum goes to nothing, therefore any vacuum leaks are irrelevent. I would make sure your fuel filter is clear and fuel pressure is at specs. These will give symptoms during peak engine demands. I would also check for codes and look at live data. You can monitor sensor signals to verify their integrity so you don't go replacing parts that aren't bad.

I believe you will find low fuel pressure. You can connect a gauge and situate it so you can monitor fuel pressure as you drive and try to simulate the problem.

 

[Jdeere562]

Sounds like an exhaust restriction. Plugged convertor? Put hand over the exhaust pipe and feel what is coming out.

I'm an old man and LIM means nothing to me. Speak English.

 

[Lubener]

Sounds like an exhaust restriction. Plugged convertor? Put hand over the exhaust pipe and feel what is coming out.

That is also a possibility. He can verify that with a vacuum gauge.

 

[MuzzleFlash40]

Sounds like an exhaust restriction. Plugged convertor? Put hand over the exhaust pipe and feel what is coming out.

I'm an old man and LIM means nothing to me. Speak English.

Lower intake manifold lol sorry

 

[ls1mike]

Did it run fine before the LIM was complete? I am going to assume it did and you just needed the intake done. You can disconnect the MAF on that and see how it runs.

 

[fsdork]

Was there a time where the engine was working properly with the new IACV? When you say you "tried that first", do you mean you took a troubleshooting step that allowed you to eliminate the IACV as a problem? Or do you just mean it's been replaced?

All of the above to ask - could the new IACV be defective or improperly installed?

 

[14Accent]

Sounds like either a severely clogged cat, or a lack of fuel volume/pressure. A weak fuel pump will idle an engine and putt around town fine, but run out of ability at higher loads.

You'll need to check exhaust back pressure with a gauge, but you could check your fuel trims with a scanner. If your fuel trims go hard positive during the lack of power scenario, you know you've got a fueling issue.

 

[chemman]

As others have mentioned, check the fuel pressure to make sure it is specification (41 - 47 psi) and the average current draw specification is 7 amps (per Delphi Tech Support).

The other thing to check are the ignition coils. Because of where they sit on the engine, the spark plug towers are prone to corrode due to moisture intrusion especially if the plug wires have never been removed.

While you are at it, check the ignition coil primary and secondary side resistances. The primary side resistance specification is 0.50 - 0.90 ohms and the secondary side resistance specification is 5000 - 9000 ohms.

I experienced similar problems with our 1999 Buick Century a few years back. The first time it was the fuel pump going bad, and then about a year later it was the ignition coils. No DTCs were set either time.

 

[D60]

IAC shouldn't come into play above idle and especially while driving on the highway and flooring it? I don't think we need to worry much about the IAC

 

[spasm3]

Sounds like exhaust restriction, I.E. catalytic convertor. But is it downshifting?

 

[Chris142]

Excessive play in the throttle cable?

 

[1444buicking]

- I agree with @14Accent on the clogged cat which is easy to test.

- We had those engines and the TPS was the source of our surging and periodic engine acceleration issues. Problems increased over time. It was tough to diagnose.

- When was the last time all 6 spark plugs and wires were changed?

- Bonus- Other tweaks you might consider after getting this problem fixed

The EGR valve and passages clog up so that is something to consider for poor running. The EGR fix was to replace the valve with OEM if you can (the aftermarket ones died quickly IME) and clean the passages of carbon. I don't think this is your main culprit however.

Check the air intake system.
- Make sure airbox and all the hoses are clamped and properly secured. Look for cracks
- Replace air filter
- Clean throttle body and butterfly
- Clean MAF sensor (requires special cleaner, don't touch lol)

 

[MuzzleFlash40]

Thanks for the replies.

It had a tune up while the gasket was being done (plugs and wires). It was running fine before the gasket so either something happened or it’s a coincidence.

A couple months ago it was idling really high so I changed the idle air control. It idled high randomly the other morning again on top of the other issues so I warrantied it out just on the chance it was a defective part.

As long as I’m not looking at a vacuum leak from the shop not installing the new gaskets wrong.

Seems like it’s something simple just tacking it down is a pain

 

[MuzzleFlash40]

Update: I unplugged the MAF to see if anything changed. It ran fine at first. About 5 minutes into the dive it started acting up again and the engine light came on. I ran the code and code P0122 “Throttle position sensor low circuit” is the code.

Could it be the TPS is bad but only acts up after the engine is warm or something. I wouldn’t imagine the MAF unplugged would trigger that specific code?

 

[ls1mike]

So what i learned from fixing my own stuff and submarines for 30 years was this. If It worked fine before you had the work done look at the last thing touched. We say it a bit more colorful in the Submarine Navy. Check every connection for bent, broken, pushed pins. Verify every plug wire is connected properly and of good quality. Verify no kinked fuel lines. The 3100 is like the 3800 in the fact a lot of times a vacuum leak won't set a code. Get yourself some carb cleaner spray around the intake and all vacuum lines see if it idles up. Coincidence is a thing but you just had the top of the engine off. Start there or take it back and tell them it isn't right. Don't chase anything else yet.

 

[1444buicking]

I don't remember what happened when we unplugged the MAF for troubleshooting.

But I do remember the TPS was intermittent. And was a problem on longer highway trips so thought it could be somewhat heat related. But wasn't always the case. But for our mystery problem, that was the core issue.

You may have a vacuum leak independently.

 

[wtd]

I would start by hooking a fuel pressure tester and seeing if it's in spec and also watch your fuel trims on a scanner. If you have a vacuum leak, your fuel trims will be positive. Anything from -10 to + 10% is considered normal but you want it as close to 0 as possible.

If your fuel trims are high and you start revving the engine and the fuel trims start coming down, that is a good indication that you have a vacuum leak.