Toyota Sienna "gulping"

catalytic-converters

#1

Hello, new poster here. Hoping someone can help!



My '98 Toyota Sienna LE has 110,000 miles and has been doing something I can best describe as “gulping,” but only in certain situations–like when I’m running about 45 mph, have to take my foot off the accelerator to round a curve, then give it some gas to pull up a moderate incline. At that point, the van seems to hesitate, shudder, “catch its breath”…and then go on as if nothing has happened. Then it might not do it again until I’m at that same spot in the road again.



I’ve taken it to a repair facility, where I descibed the problem as sounding and feeling “respiratory,” not “physical.” In other words, it didn’t seem like anything related to the transmission or drive train. (But what do I know.) So far, they’ve replaced the plugs and wires…cleaned the throttle…and replaced the fuel pump and oil pump. I’ve had it back in every morning this week, because it KEEPS doing it, despite everything that’s been done. The repair guys say they’ve driven it in all kinds of conditions, hooked it up to the computer, inspected it top to bottom…and still can’t pinpoint the problem, or get the van to replicate the symptoms I’ve descibed. They say it keeps checking out OK, and that they’ve done everything they can think of that might be causing the problem.



As I left my last visit, the service manager (who had just got back from test driving the Sienna himself) said it was a real head scratcher, but he didn’t think there was anything seriously wrong with the vehicle, and that he would advise for me to keep driving and don’t worry about it, unless it becomes much worse. (He said he had a suspicion it might be the torque converter, but he absolutely would not reccommend getting into that unless the problem progressed substantially.)



This doesn’t sound exactly like 5-star automotive advice to me. I’ve spent just over $1,700 for all the work so far. and the problem persists. I’m worried that, one of these mornings, it’s just going to konk out completely and leave me by the side of the road.



Can anyone advise?



Thanks, I’m desperate!



NashVega


#2

Mechanics would usually say your truck was “hesitating” from MISFIRE. Sometimes, a bad spot on the throttle position sensor (tps) develops at off idle position. When you release the throttle, at 45 mph, the throttle (NOT the engine rpm) goes to the idle position. When you press the throttle again, the tps goes through the bad spot, and the computer, which receives this bad signal, doesn’t know what is going on. So, it waits (hesitates) a moment, or two, for other sensors to fill in the missing information. // When the truck resumes speed, is the engine rpm the same or does the transmission seem to shift out of overdrive, or high gear? You might need a transmission shop look at your truck.


#3

Thanks HelloKit,

I haven’t paid attention to the RPMs when it’s “gulping” then recovering, but I don’t experience any loss in momentum, and it doesn’t seem like the engine is revving up or relaxing. But your suggestion about having a transmission guy look into it is a good one. I just hate the thought of spending even more $$, especially if I can’t get a definitive diagnosis. Interestingly, the first thing the shop did, when I brought it in initally, was treat it for “misfiring” by replacing the plugs and cables. And that didn’t fix it. I would have thought they would have looked at the throttle sensor, and any other sensors that had to do with the working of the engine. I’m not very auto-minded when it comes to what’s going on under the hood, so I feel somewhat at the mercy of a mechanic when he says, “Here’s what we need to do.”

Thanks again, and any other suggestions you can offer would be appreciated.


#4

The shop didn’t do wrong with changing the spark plugs and wires. If the fuel filter is NOT in the gas tank, they should have changed that, too. They probably hooked a scan tool to it. I, still wonder if they observed the voltage pattern of the throttle position sensor throught it range, or, just at one point? The scanner would show if any misfires (in excess of 2%) had taken place. It would, also show if any codes are “pending”. “Pending” means the computer is waiting for the fault to happen again. It would, then, report it as a trouble code, and turn on the check engine light. Maybe, you’ve seen the check engine light flash when the engine takes its “gulp”? When the scan tool was connected, the throttle position sensor (tps) voltage pattern should have been observed while the throttle was being slowly opened and slowed closed. The values should vary smoothly, up and down. Is the check engine light coming on, or flashing? If it is, many of the auto parts stores will scan the codes for you (free). Get the codes and bring them here for comments.


#5

Thank you again, Hellokit. I’ll keep this thread updated as I dig deeper into the problem. Today was smooth sailing, no blips or slips at all. I’d like to interpret that as good news!