Why does the engine 'skip' when I'm breaking at a red light?

February 8, 2010 12:08 PM

My car 'skips' when I'm stopped at red lights. Please help me try to diagnose what's ailing my sad, old car. YANAM/YANMM.

I have a 1993 Toyota Camry with 203,000 miles on it.

The weird thing that's happening: when I stop at a red light, pressing the break down, there's like a 'skipping,' is the best way I can explain it. Like while I'm pressing the break the car seems to sort of jump, if you will, sporadically. Sometimes just once, sometimes many times in a row. The car doesn't move forward of course, but it's almost as if it's trying to?

A bit more about the car: About three years ago, I hit a free range cow in Southern Utah. Put a lot of money into the car to fix it, and it's really never been the same.

In the past 3 months I've had 1) new brakes installed; 2) a new radiator and new fans installed; 3) and most recently I had the timing belt/water pump kit replaced.

I was told by the mechanic after the last fix that everything looks good to go and I should be fine to drive it for a couple more years.

Getting a new car at this point is not so much an option. I don't drive it all that much, but I do need it on occasion.

Does anyone know what this weird skipping/catching thing could be? Alternatively, does anyone know a great mechanic in Portland, OR? The same guy has been working on it, and while I really like him, a second opinion might be necessary at this point.

Thank you Hive.

posted by Lutoslawski to travel & transportation (19 answers total)

Try checking to make sure all of your plug wires are firmly attached to both the engine and the distributor cap.

It might also be a loose engine mount bolt, so I would suggest checking to make sure all of those are tightened.

Do your breaks feel firm when you push down on them? Or does the pedal go all the way to the floor when you first push it, then become harder to push down?
posted by strixus at 12:12 PM on February 8, 2010

That happened to my girlfriend's car and it was the sparkplugs. I'm no mechanic.
posted by chrillsicka at 12:12 PM on February 8, 2010

Does it feel like the brakes aren't catching properly and that's causing the skipping? Could be a brake fluid leak. Definitely get it checked out, though.
posted by InsanePenguin at 12:16 PM on February 8, 2010

The brakes feel firm when I press them. It doesn't seem to be so much of a problem with the brakes as something more perhaps with the....engine? Or some such.
posted by Lutoslawski at 12:26 PM on February 8, 2010

Ok, if the brakes feel firm, then it is most likely an issue with either your plug wires or your spark plugs.
posted by strixus at 12:32 PM on February 8, 2010

I had my spark plugs replaced in 2008. Could they wear out that soon? If I need new spark plugs, what am I looking at cost-wise? And if the plug wires need fixed?
posted by Lutoslawski at 12:38 PM on February 8, 2010

Brakewise, it could be the brake booster. Does it happen regardless of how hard you press the brakes?

Braking force is generally amplified by the vacuum the engine produces from sucking in air to burn. That vacuum gets stronger and stronger the harder the engine works. When you're stopped, there's much less vacuum available. The car is supposed to have a check valve to keep the vacuum pressure up even when at rest or if the car is switched off, but it can fail or the booster itself can leak air. Your brakes would get weaker in that situation.

Otherwise, could be a problem with the automatic transmission (if so equipped) or maybe a bad motor mount?
posted by paanta at 12:39 PM on February 8, 2010

I had an early circa '90 Chevy Corsica that had a problem similar to this. When slowing to a stop after having gotten up to highway speeds, it would try to jump forward a few times, and sometimes the engine would die. I got the impression that it was a pretty common problem with the Corsicas, and is due to a part called a TCC Solenoid.

I'm not seeing the same kind of helpful google results for Camry TCC Solenoid, but it might be something to keep in mind.

I'm so very not a mechanic.
posted by GeekAnimator at 12:40 PM on February 8, 2010

Just pull the wires out and see if the terminals are corroded. If they are AutoZone used to have replacement wires that are lifetime warranty so when it happens again you can just go trade for new ones. Spark plugs are cheap too so it's easy to test this. The wires should be clean and shiner if they're new.
posted by jeffamaphone at 12:43 PM on February 8, 2010

I had my spark plugs replaced in 2008.

Probably unrelated to your problem, but you need new sparkplugs. I change mine out about every 10,000 km, it's good for fuel economy and engine performance even if not necessary.

A set of new sparkplugs should cost you something like 20 dollars (at least that's the equivalent cost around here), replacing them should take about 10 minutes of work for your mechanic if you don't have a wrench or don't want to do it yourself.
posted by Dr Dracator at 1:05 PM on February 8, 2010

Your car most likely has on board diagnostics.
You can buy a code reader for about $25-30.00 at most auto part stores to pull trouble codes. On some cars, you can even pull codes without a tool (usually involves jumpering a port under the dash and counting the number of blinks on a dashboard light)
posted by zombiedance at 1:23 PM on February 8, 2010

I dont know if i agree about spark plugs every 10k. Modern engines and gas are so clean that they don't really foul. It takes a long time to wear out a spark plug these days. However they do need to be checked/cleaned/regapped every couple of years just to avoid the plug galling into the cylinder head and becoming impossible to remove.

Anyway I would guess you have a vacaum leak somewhere, most likely the brake booster.. could also be an electrical issue, possibly from something relating to the crash or a mechanic forgot to hook something back up (really, really easy to do).
And finding those is a nightmare. Look for pinched/damaged rubber lines or wiring, of which there is no shortage of in this car (lines and wiring, I am hoping the damaged part IS actually in short supply). A problem like this can go a long time with no real problems or break tomorrow (if it does break for sure than it becomes much easier to find). Good luck.
posted by bartonlong at 1:24 PM on February 8, 2010

IANAM.

My 1993 Volvo 240 does exactly this, but only when the engine is very cold-as in, the temperature must be below freezing, and the car must have been turned on from a cold start in the last ten minutes. I shift into neutral at stoplights (automatic transmission), which solves the lurching symptom depending on temperature, but not the underlying cause, since the engine still rhythmically races until it is warmer. Giving it a little gas tends to settle it down.

I have never bothered asking my mechanic about it. I suspect that it is a problem with the fuel injection system: the car isn't getting enough gas (running too lean) at idle when it is really cold, and the computer is alternately dumping too much fuel in or not enough to try to compensate. For me, it's surely not a brake problem or transmission problem, since the problem continues when those variables are removed from the equation. I am just trying to describe my experience; I don't know enough about cars to know how well it will translate to you. I hope my answer is helpful.
posted by Kwine at 1:56 PM on February 8, 2010

Are we talking jerky juddery stopping as you slow down for the red light, or are we talking hiccups and bumping and engine coughing while you are sitting at the light with your foot on the brake? Because those two things will have different possible causes.
posted by flabdablet at 3:48 PM on February 8, 2010

Are we talking jerky juddery stopping as you slow down for the red light, or are we talking hiccups and bumping and engine coughing while you are sitting at the light with your foot on the brake?

Not until I'm stopped and sitting at the light with my foot on the brake. In fact, it usually takes a few seconds of being stopped before it starts. If the light is short, sometimes it doesn't happen at all.
posted by Lutoslawski at 4:50 PM on February 8, 2010

Seconding vacuum leak. Likely at the brake booster. It could be the booster diaphragm starting to fail. If so, eventually you won't have power brakes anymore. If you're lucky, it's the hose that leads to the brake booster.
posted by dalesd at 3:13 PM on February 9, 2010

You could have a vacuum leak, a sticky idle air control valve, or some minor ignition related failure.
Does the car accelerate normally or does it hiccup, stutter, or accelerate un-smoothly?
Is there ever any hard-starting? That is, does the car crank for a prolonged period of time before finally firing up and running?

If you answered no and no, I'd guess Idle Aair Control Valve. An ignition problem (plugs, wires, cap, rotor) will often cause hard starting and poor or uneven acceleration and isn't usually something that occurs strictly at idle.

So...
When you're stopped, the throttle valve is closed. That means that no air is getting into the engine. If there's no air, then it can't burn fuel and the engine can't accelerate. When you step on the gas, you open the valve and allow the magic to happen. So, given that, when the car is at an idle and the throttle is closed, there needs to be a way for just enough air to get into the engine to keep it running. This is where the Idle Air Control valve (or IAC) comes into play. Given a number of other inputs, the onboard computer actuates a bypass valve that's attached to the throttle body (the assembly that contains the throttle plate, return spring, throttle position sensor, etc) and the computer thereby meters a specific amount of air into the engine.
Now, after many miles it's typical of throttle bodies to become gummed up or develop carbon deposits. There are a lot of other vapors besides air swirling around in the throttle and intake manifold and this miasma consists of hydrocarbons, oil vapors, and crankcase vapors. All of this stuff will eventually clog up the fine-tuned ports of IAC and also interfere with its electromechanical operation. It's just a solenoid or plunger valve and if can't open and shut correctly, it'll cause a problem like what you're describing. When it gets really bad, it can stall the engine instead of just stumble of misfire.

It could be a vacuum leak in your power brake booster as others have mentioned. Possibly, when you press the brake pedal, the booster diaphragm flexes and enlarges a pinhole, allowing unmetered air into the engine, resulting in a rough idle. However, due to the location and shape of the booster assembly, a common and accompanying symptom of a perforated brake booster diaphragm is a pronounced hissing or whistling noise when you press the pedal as the engine vacuum rushes through the tiny hole in the booster. The brake booster is a big drum shaped thing that is right in front of the driver, on the other side of the firewall. The whistling of a leak is usually amplified to the driver. You may also begin to notice a difference in the way the pedal feels. The brake may become firmer over time as the vacuum assist effect is diminished as the hole in the booster diaphragm grows.
posted by Jon-o at 8:27 PM on February 9, 2010

Jon-O to the car rescue once again! Wow, thanks man. That's a great answer. So yeah, there is not any accelerator weirdness, nor does it ever hard start. So I'm guessing it is probably something with the IAC. Should I just take it to my mechanic? Do you have any idea how much getting this fixed may cost?
posted by Lutoslawski at 11:23 AM on February 10, 2010

Well, what's going to happen is that when you tell your mechanic that that car runs rough but only at idle, he should know right away to pull off the big rubber bellows that connects the air filter housing to the throttle and look in there for ugly carbon deposits. You'll probably wind up paying an hour or less of labor for a thorough cleaning of the throttle body and IAC passages or the valve itself.
That valve itself can cost up to about $200, so I'd check its actuation before replacing it. I'd remove it, clean it, and jump power to it to make sure it clicks nice and loud.

So, this'd be a first step. If it were me, I'd clean the throttle as a preliminary measure just to rule it out in the event that further diagnosis is needed. Gotta start with clean slate, right?
posted by Jon-o at 3:00 PM on February 10, 2010